At first glance, the app TikTok looks like something I’ve seen before. With its short, vertical videos that play on an endless loop, TikTok is reminiscent of Vine, the defunct short-form video-sharing platform. Options to view my profile or search the app are pinned to a bar on the bottom. Share, comment, and “heart” options are stacked on the right. To create a video, I’m prompted to click the large plus sign centered on the bottom.

Before filming anything, I swipe through TikTok’s “for you” feed. It’s a vertical string of featured video clips that I can only assume were recommended because they’re performing well among the app’s teen user base.

In one of the first videos I come across, a 16-year-old girl in braces dances in her bedroom. The video is tinted pink (TikTok’s answer to the Instagram filter) and Chris Brown’s verse on O.T. Genasis’ “CoCo” plays on loop. You picture perfect let me centerfold you, alright, alright. The bottom of the user’s shirt is folded up, baring her stomach. A few seconds into the clip, she begins to rub her crotch while lip-syncing the lyrics: All my bitches got asses.

The video plays on repeat. In the comment section, the app encourages users to “say something nice.” A few viewers have responded with sexually suggestive comments, variations on a theme (“rub that thing baby,” “let me rub it,” etc.). Within a few hours of uploading the video, the user has disabled comments and made her account private.

Since the early web blogging days of Xanga, teens have sought new ways to express and embarrass themselves online. TikTok accomplishes both those things and then some.

Until last month, TikTok was best known in the United States as the Chinese equivalent of Musical.ly, a lip-syncing app that burst onto the tween smartphone scene in 2014. Developed in Shanghai by two Chinese entrepreneurs, TikTok is one of the first Chinese-owned social media startups to build a significant user base outside China. Along the way, it has grown into one of the world’s largest virtual stages for adolescent expression — that is, if “adolescent expression” is often a euphemism for sexually suggestive dancing set to explicit lyrics.

TikTok was the most downloaded iPhone app in first part of 2018. It received more downloads than YouTube, Instagram, or Facebook.

Last year, ByteDance, TikTok’s parent company in Beijing, reportedly paid between $800 million and $1 billion to acquire Musical.ly. Just last month, ByteDance shut down Musical.ly and merged its user base with TikTok’s in a move to establish the ByteDance brand in the U.S. market. Today, TikTok has upwards of 500 million monthly users worldwide. It was the most downloaded iPhone app in the first four months of 2018, garnering more downloads than YouTube, Instagram, or Facebook. Most important, it has gained a foothold in the psyche of tomorrow’s young adults.

TikTok’s user base is young. Demographic breakdowns following the merger with Musical.ly are hard to come by, but earlier this year, DigiDay reported that 50 percent of Musical.ly’s user base was between the ages of 13 and 24. And what kind of content do today’s teens create? Mindlessly repetitive memes. Makeup application contests. Fortnite highlights. Comedy skits that make the app feel almost exactly like Vine with built-in background music. Many of the videos I watched were filmed in bedrooms and featured just one person. Which is to say that TikTok feels more like an app you’d use when you’re bored rather than a way of keeping up with friends or news.

Despite its amateur vibe, some users have found a way to parlay success on Musical.ly and TikTok into moneymaking careers. Fifteen-year-old Jacob Sartorius turned his viral lip-syncing videos into a record deal. Sixteen-year-olds Lisa and Lena, two identical twins from Germany, have the most popular account on TikTok. It helped them launch their own clothing line.

It’s too early to tell if TikTok is here to stay. But with realistic pathways to microcelebrity, millions of users aren’t going to sit around waiting to find out.

On user-generated content platforms — TikTok, Twitter, Instagram — the algorithm determines what users see and, ultimately, how they behave. Engineers and product designers deliver and amplify content that meets their business goals.

In a subtle but consequential sleight of hand, TikTok’s product designers set the “for you” page as the default landing page for all users. This is the equivalent of Twitter and Instagram directing all visitors to their “moments” or “search” pages. On TikTok, the “for you” feed is filled with videos from anyone with a public account. Where Twitter and Instagram encourage you to follow your favorites and build your own feed, TikTok uses its algorithms to show you what’s popular. Although the app maintains a separate feed dedicated to accounts you follow, this feed is not nearly as popular. One study of TikTok found that less than a quarter of users had ever clicked on the feed of accounts they follow.

TikTok’s “for you” page makes sense from a business perspective. It immediately hooks new users with content proven to get them to engage. While most apps use this tactic to some degree (Facebook and Twitter pepper their feeds with posts “you might like”), TikTok uses it more than most.

Taylor is a 17-year-old TikTok user. She started out on Musical.ly and transitioned to TikTok after the two apps merged. Hardly any of Taylor’s videos have received more than 10 likes, but a few weeks ago, a video of Taylor lip-syncing to Pleasure P’s “I Love Girls” was featured on the “for you” page. It’s not an interesting video. It’s just Taylor staring into her phone’s camera and mouthing the words to the song: She take my shirt off, put my hands up. I pull her hair back, you know she like it rough.

Taylor’s video has received more than 2,400 likes so far.

Taylor says she didn’t realize her video had made the “for you” page until she started getting more likes than usual. Another tip-off: Comments from users who didn’t follow her.

The app’s content delivery strategy sets its users up to receive unwanted comments.

“Some guy was like, ‘I’ll do all that to you the right way,’ which was weird,” Taylor tells me. Compared to comments on an app like Instagram, Taylor says TikTok’s comments are “probably more creepy.”

Underage girls may receive a disproportionate number of creepy comments on the app, but there are other forms of harassment on TikTok as well. One user, a 26-year-old man, appeared in my “for you” page a number of times because of his viral collaborations with other users. The user — who is bald and dances with reckless abandon — received comments asking if he has autism (he doesn’t) and telling him he is the reason adults shouldn’t be allowed to use the app.

The app’s content delivery strategy sets its users up to receive unwanted comments. Any user with a public TikTok account can be exposed to hundreds of millions of strangers without warning (Taylor says TikTok did not tell her in advance that she would be featured). Tweens create content, hoping for their 15 minutes of fame, only to be creeped out when it arrives.

“On Instagram, you can have a public account, but your content probably won’t be put in front of people you don’t know as easily as on TikTok,” Christine Elgersma, of Common Sense Media, a parent-focused media watchdog, tells me.

TikTok isn’t the only platform where underage users are hypersexualized. But the behavior is more severe on TikTok because teen users create videos that respond to the lyrics of explicit songs. “I think because TikTok is using music, and because popular music often has sexual innuendo, the app skews more mature,” Elgersma says. American teens have always sung along to explicit lyrics, often without knowing what they mean. Now an app helps them do it for a built-in audience of millions.

When I ask Taylor why she thinks that video of her lip-syncing to “I Love Girls” was featured on the “for you” page (as opposed to any of her other videos), she says, “I don’t know, probably just the music I used.”

TikTok’s parent company, ByteDance, has been dealing with content concerns since before the Musical.ly merge. In March, writer and parent Anastasia Basil published an essay on this website titled “Porn Is Not the Worst Thing on Musical.ly.” In the essay, Basil warned fellow parents about the app’s “dark side.” Some users, Basil reported, upload sexually suggestive and disturbing videos under hashtags like #thot, #selfharm, #cutter, and #anorexic. As Basil writes, “Setting your child’s account to private may make him invisible, but he’s still there, fully present, taking it all in.”

Following the article, BuzzFeed News found that users could also search for #proana and #mutilation on the app. When Buzzfeed News reached out to Musical.ly for comment, the app responded by removing the ability for users to search for those terms. Now when users search for terms related to self-harm on TikTok, the app directs them to the National Suicide Prevention Lifeline.

Meanwhile, earlier this summer, the Indonesian government temporarily banned TikTok for containing “pornography, inappropriate content, and blasphemy,” according a report in Reuters. The Indonesian government issued a list of demands that TikTok needed to comply with for the app to be reinstated. ByteDance acquiesced and promised to remove “all negative content” from the app by setting up a team of 20 content moderators in the country. A week later, the government overturned the ban.

But ByteDance hasn’t always responded well to outside criticism. In July, a relatively unknown YouTuber named PaymoneyWubby posted a video criticizing Musical.ly. (This was before Musical.ly and TikTok merged.) YouTube took it down in August, after ByteDance claimed the video used copyrighted footage. The video in question, “What Kids Really Do on Musical.ly,” is a comedic screed against the oversexualization on the app. At one point in the video, PaymoneyWubby, who asks that I not use his real name, reacts to two different Musical.ly clips of underage boys having sex with an invisible partner on the floor. “This is for kids?” he asks, staring at his computer in disbelief.

After his video was taken down, PaymoneyWubby uploaded a second video expressing his bewilderment with ByteDance’s copyright claim. YouTube is full of Musical.ly and TikTok compilations from unofficial accounts that qualify as far more egregious examples of copyright violation, he claimed. Thanks in part to a flood of traffic from Reddit, PaymoneyWubby’s original and follow-up videos have now been watched more than a combined 1.5 million times.

After a short review, YouTube reinstated PaymoneyWubby’s video, but he still believes he was unfairly targeted by ByteDance for speaking out against the app.

“I do believe ByteDance took down my video in an attempt to silence my criticisms,” PaymoneyWubby tells me. “If they did it to me, I can only assume they’ll do it to someone else.”

TikTok did not respond to a request to comment for this story.

In a world of user-generated content, young people have incredibly powerful tools to broadcast their innocence to the world. As adults, our first reaction is often to chastise teens for being shameless and rash, but anyone who’s once been young knows that usually falls on deaf ears. Alternatively, we blame other parents, expecting them to act as content moderators for their own children. We expect parents to be experts in newfangled apps. We expect them to step in where irresponsible product designers and corporations won’t.

In a world of user-generated content, young people have incredibly powerful tools to broadcast their innocence to the world.

Meanwhile, app creators receive comparatively less scrutiny. It’s not the platform’s fault when an underage user broadcasts a provocative dance from her bedroom after watching hundreds of similar videos that have been recommended to her — it’s her parents’ fault for not turning on the optional (and hard to find) parental controls. It’s not the app’s fault when a 10-year-old boy DMs back and forth with an adult stranger who has liked all of his videos and told him how beautiful he is — it’s his parents’ fault for not teaching him to ignore unwanted attention.

“We now live in a country where it is seen as abnormal, or even criminal, to allow children to be away from direct adult supervision, even for a second,” writes Kim Brooks, author of Small Animals: Parenthood in the Age of Fear. Brooks is referring to parents’ fears of letting their children play in the park alone or ride their bikes with friends. But as our social lives play out online, it’s easy to imagine a future where parents spend as much time policing platforms as they once spent supervising playground outings. Barring a dramatic change in how these apps are designed, it will be parents, not platforms, who bear the burden of both limiting and monitoring underage users’ online activity.

TikTok is not the first app to raise these concerns. It’s the latest in a long line of platforms that depend on users to not only consume content but also create it. Luckily for the apps, we never seem to run out of ways to embarrass ourselves.