Bio dad "not in picture"

I'm glad this question was asked, because it is something I have always wondered. As a follow-up question, "If the father has never been in the picture, will cw's still search for relatives on the father's side? Would they give serious consideration to someone from the father's side if one suddenly showed up?" I have always felt like the biodad that's not in the picture creates far too much of an unsettling mystery in the life of the child and the fp.