Don't involve his friends or family. This is solely about him and his trafficking involvement. If you talk with his friends and family you will likely put yourself in real danger in addition to alienate yourself from your shared social network, since people tend to take sides in these situations.

I really would get the police involved. Ask them to investigate the strip club's cameras. Every strip club has them. They can also run a background check on this guy and the women who work there. Do not say ANYTHING to his friend's or family. Do not involve them. They would likely become collateral damage and also be in danger if your friend is indeed involved in human trafficking out of that strip club. Really, you have to get the police involved somehow. Or a watchdog group that can monitor this guy in this strip club a la steakout. There are groups that do that sort of thing, that lead to busting up trafficking circles. But please leave that guy's friends and family members out of this situation.