I was also adopted by my step-father. My biological father was never really in my life, although I remember him vaguely. Occasionally, I'd see his parents and sister. I always thought that when I was older I'd want to meet him, but I don't. (I'm 35.)
My step/adoptive dad is my dad, his extended family are my family, and I have three younger brothers. I don't consider my biological father my "dad," and am not interested in meeting him or his family. (I do know who they are though, so it's not like a closed adoption where you have no information about where you came from.)
For me, it's not a loss that I have no contact with my biological father and his family.