Replying to How to punish this guy?

a couple weeks ago i was trying to buy bud downtown, i ran into this fatass who said his friend down the street had really good deals. i followed him there, and (retarded, i know) fronted him 40 bucks because he appeared to be going right into his friend's apartment, and he gave me his resume as collateral. i knew, since it was just a hard copy, that this had little value to him but i somehow trusted him. anyways, he wasn't back in 30 seconds as promised, and i knocked on the door like 30 times. finally after like 10 minutes i gave up and left. apparently this dude makes his living doing this, and he just escapes out the back door of the apartment building. anyways, this gigantic guy is very easy to recognize, and i found him today taking money from underage girls claiming he was gonna buy them alcohol. i confronted him and displayed quite a bit of anger but could not get him to pay me the 40 bucks he had stolen. his posse acted up on me and then he left. i have a couple of friends who know about this guy and what he does, and luckily i know his name and where he's from because he was stupid enough to hand me his resume a couple weeks ago at the incident. is there any way i could fuck him over by reporting him to the cops as a thief and underage alcohol distributor (from only a witness standpoint) if i get some of my friends to attest to it? or is it impossible to prove and could it potentially backfire? this guy wont stop jipping kids unless i do it, but i need NS to approve of talking to the popo's. also if i see him again i could blackmail him with a 911 call, in front of his face to get my dollars back.