How do I get his contact info?

I have a webdesign company and I just finished up with a client (all through email and phone calls). He paid me 20% down for a small $240 job. I completed all of the work and he was to pay my invoice I sent him. However, I haven't heard from them in a week.

Now two things, I was comfortable handling this not in person because I won't kill myself if I don't get paid. But...

1. The lead person involved is young (I think he is just finishing high school)
2. The site I made the logo and custom background for has a lot of potential for profit and traffic.

So worst case scenario, can I do anything, get him on copyright, etc? I'm just curious. This is the first of 30 clients this year who has presented a problem (thank goodness)

I know his host, and registrar.