Only if it gets big, and in that case, it can be avoided by analyzing transactions and discovering uncommon behavior. Good transparency in who does what and gets how much for it could also help. Nobody would use the app for money laundering if the police can just look at the logs.
Dirty money across many accounts -> given to account "performing" the dare -> withdrawn as bitcoin -> sold on exchange.
I like the idea, but based on some of the things you're doing (holding funds, taking credit cards and giving out bitcoins) and your response above you are stepping into a world of regulation and fraud that you are completely unprepared for. I seriously suggest you contact a lawyer before you commit a felony.