Some free resources for searching for your birth father include Internet search engines and social media sites that offer search features and family members that might volunteer information. Libraries and veteran's associations are also organizations that may offer information searches at no-cost.
Family members of both the adoptive family and the biological family, if known, can act as free resources to provide information on the biological father and his whereabouts. If the biological mother does not support the search, more extended relatives might cooperate to provide information. In addition, organizations that the father might have associated with, such as a high school or an employee union, might provide valuable information that the organization maintains on file.
A public library also likely has newspaper records and other resources available for free. Asking a librarian personally might also yield information because the librarian might be a long-time resident of the area with personal knowledge of the situation. Internet search engines might provide valuable information based on the adopted father's name, occupation or the location of the child's birth. If the biological father served in the military, a veteran's association might offer the man's identifying or contact information.