This should be an entirely personal decision and anybody exploring this issue should be guided by their heart and not the advice of others.
My brother and I are both adopted (obviously from different biological parents as will become clear) - he has chosen to seek out his biological parents, while I have not yet. Neither of us regrets our decision and we are both entirely comfortable with that.
Thankfully, our adoptive parents supported our choices in both instances and I admire them for that. It is extremely brave of them to take in two little characters, raise them, love and educate them, and still support any interest in finding "other" parents! Unselfish love in the extreme!