Coming from a bill collector - no, there is no good free site to track somebody down.
If you want the best, it's Lexis Nexis as they took over the Accurint platform a few years back. Other good pay site is insightcollect.com but again neither of these will help you since they're subscription based location services.
I know somebody who does skip-tracing but its for a price. The guy is good and has 2 contracts that i know of with national lenders to find people, although his specialty is finding employers and bank accounts. I don't know what basic info you have on the guy you are looking for (ss#?) but if you want pm me and i'll pass along the skiptracer's contact info. Keep in mind if though i'm not guaranteeing this guy's results. I don't even know what he charges for a locate.