In the past, lots of scammy/spammy apps grew fast by bribing the user to invite all of their friends etc. But you have to grow pretty fast for FB to see this and delete you, I doubt anyone can replicate that growth now since lots of the viral features were removed. Seems like the only way to mass a huge audience is to buy it with FB ads.
My strategy for adopting the new api was to move the userbase from an existing app to a new one. Fb deleted the new app in the middle of the migration.