If the biological father's name is known, finding him could be as simple as completing an Internet search. If it is not known, DNA testing can be performed. If the biological father was a donor at a sperm bank, he may be protected by anonymity clauses; however, a letter can be sent to him in care of the sperm bank, who will forward it to him and allow him to decide whether he wants to remain anonymous.
A biological father's name can be obtained by asking family members or checking to see if his name is on the birth certificate. Using an Internet search to find a biological father can be difficult depending on the popularity of his name and the amount of information he has released to the public. Use any information family members can provide to narrow down search results, such as the college he attended or the profession he practices.
DNA testing is as simple as swabbing the inside of the cheek, preparing it as the purchased kit advises and sending it to an organization that processes DNA. Returned results include close matches that, when reviewed statistically, most likely share common ancestors. While this may not return the biological father's identity immediately, it will help to fill in the family tree, which can then be researched to eventually produce his name.