You think marketing your app is hard? Try finding a profitable source of users for a social casino app. In contrast to real-money gambling apps, social casino apps let players try their luck at slots, video poker, bingo, and other games of chance – without wagering real money. These are apps are extremely popular, claiming 7 of the top 25 grossing slots in the app store right now. They’re also big business, with a market estimated at $4.4B in 2017. The trick is that the revenue is extremely concentrated in a small number of players: the VIPs, a tiny percentage…..