If this dude used USPS thats mail fraud.
What is his full name and mailing/shipping address.
Send a demand notice to the address Return Receipt Request and list Prize Notification on sender info of Receipt. That way if hes not there he will be sure to go and pick it up at the post office.
Report the fraud to your USPS postal inspectors office asap.
Try looking up his name and address in the white pages. If you can't find him maybe you'll find one of his realitives. If you get a realitive get all the info out of them on him you can. If they don't provide you info don't threaten just ask them to have him contact you asap. If all fails then tell them what has happened and let them know what he has done.
Just remember you are on a fact finding mission right now. Be polite and gather all the info you can on this guy in hopes to contact him.
Its guys like this that really get under my skin.
Hope it works out for you.....