If you don't have an address or a phone number and cannot find out the name in the telephone directory, cannot pay for an ad in the newspaper (assuming that the relative reads those ads), cannot track the relative on facebook, don't have an email address, don't have a contact of any relative who has the contact of this relative, try to approach the Police department. Maybe they'll be able to help you.

Sometimes the "skipease" web site can help, but it's changed a lot and now sometimes refers you to sites which charge money for information they claim to have. Never pay money to those sites; they are scams.