Finding estranged family members without paying?

I've been searching for the contact information of my estranged father, but am having difficulties finding it without having to pay. His phone number is unlisted, so using a basic directory does not work. Obiviously, there are sites that will run a search, and give information (email, address, etc)..but I can't seem to find one that doesn't require payment. It's a bit frustrating, seeing as I know that these sites are bring back returns on my search. Does anyone know of any truly free sites through which I can get this information? Thanks.