I don't know that I would try to recover the bike - but I would be interested in seeing bike thieves put out of business.

Thing is ... no way of telling if the guy selling the bike now knows it is stolen. It may have gone through several hands by now. I would also be worried about the grief I might cause someone who does not know they are selling a stolen bike, and indeed may have no way of knowing that - particularly if no police report was filed.

I would be tempted to scope out the situation in person, but it the seller is the thief, that has it's own hazards.

Interesting conundrum ... also ... how sure are you that the kid of friends did not pawn the bike for Kraft Dinner? Or something ... else?