The Five Types of Virality
Josh Elman

Awesome post; sums it up perfectly for any startup planning for viral growth tactics.

I would add “Heavy positive PR, which leads to the fear of missing out” — this usually happens with powerful brands, e.g. PokemonGo or Apple when launching new products.

Pokemon Go had the “infectious” virality into it also. The fact that when you join you have to choose a team and cannot change it, it forced a lot of people to race on referring their friends to make sure they join their team — which empowered their virality.