its probably true that hurting him would give u a great sense of satisfaction... but it would probably leave u in a worse position (either by being prosecuted or getting beaten up at a later date)... i'd say just confront him, be stern, tell him what u know and ask him what he is going to do about it. then react to what he does, he might be very apologetic and give u the money or something.
also, if he is a friend of a friend, get ur friend involved, get all ur friends involved, tell this guys' friends who u know reasonably well, get them to boycott this guy cuz if he did this intentionally i wouldn't want to be his friend.