From technical standpoint, Facebook search is ineffective because there are more than a billion users with trillions of posts. When you search for something globally on Facebook, you get results based on an algorithm that weighs them. It is similar to Google search in that regard. So you may know that you or your friend posted something with certain words, but Facebook search may not return the result because the algorithm thinks it’s not important enough.

I wrote an iOS app SearchForPosts that stores an index of all posts, photo captions, album and video names and descriptions and comments on the device. Then it uses the index database to perform the search and retrive the actual posts from Facebook.

Granted it can’t search the entire Facebook user base, but it is very effective to search for your own posts or posts of your friends that also use the app (due to technical limitation) and pages that you like.

More info on the app can be found here: http://searchforposts.com