At Chatango we just gave up on our Android app. We don't have a report button because we don't want users to gang up and falsely report profiles. We are counting unwanted incoming conversation blocks and take action based on that, and have hierarchical moderation in each chat. That was way beyond what we could explain to the play store policing bots so about $500k in development was trashed by Google, we went website only, because it's an uphill battle. We have tens of millions of users.