What is the secret to creating a viral Facebook app?

Answer 1

jerks like you should find something else to do

Answer 2

Create something that users actually want to use. Either something that's fun or challenging and helps them meet their goals. Don't just make it an obvious marketing ploy because we can see right through that, honest. If the app is something I want to use, I don't mind looking at some ads while using it. But if the whole thing is just created to show me ads and make me take surveys, I won't waste my time.