How to locate a "possible" son

When he is of legal age - generally speaking, you can apply for his adoption records. What that would provide you is his new adoptive name. HOWEVER, saying that I think you are going to need more details and in the mean time I would focus on trying to find the child's biological mother and trying to clarify what happened and if she is willing to share further information. Once you do that -- and if you obtain the name of the adoption agency, you would probably be welcome to send a letter to your child's family, with updated medical history, a picture and an invitation to contact should his parents wish that to occur.