don't wait to long, or that bike is gone. sooner or later someone is going to realise that it's worth some bucks and get rid of it, then it's history.
get onto the cops and hassel them to chase it up, get onto the school this kid goes to and hassel them to chase him up, get hold of the kid and hassel him up.
leave it much longer and you won't even find the parts, let alone the bike.
get your finger out dude, and get on it.