I've spent many years hunting people down that were trying to hide because they owed me money. In all probability, these would be cell numbers and therefore very difficult to associate a number with an address. However, you can try this:
http://www.reversephonedirectory.com/
and give it a shot.
do you know the guys name?
still have his phone number?
have a different lady call him and very mysteriously ask to meet him at the cafeteria (local college or university). She should describe what she will be wearing, and then when he approaches her, you grab him from around the corner, along with your GF who can ID him. Grab him by the scruff and haul him into the deans office. He won't pay you, but the dean could put him on academic suspension.
Pretty hick, but it sometimes works, especially if the kid thinks the chic is some kind of secret admirer. She should call from a different cell# also.