A very personal issue, and a brave thing to do I think jofeb04.
My brother and I are both adopted (no blood connection) and are very lucky to have had the privelege of fantastic adoptive parents who made sure we both knew we were adopted, but very much wanted. We always had access to whatever info about our birth parents that was available, and told we would be supported if we wanted to go further in finding them.
Even with that background, my brother and I have different views. Whilst he always felt that he wanted some kind of explanation from his parents (long term relationship but very young, didn't find out until almost 6 months gone), I always felt I had enough information about my identity to not need contact with bm(no bf - effectively one night stand). I respect her decision - if she contacted me, I would meet her but I wouldn't go looking for her because you just don't know what to expect - she never told any family or friends she was pregnant or had given birth. She could have kept the secret.
Equally though, until I gave birth myself I had a fairly romantic notion of what she went through and the decision she made. After having my own children, I respect her even more but respect and like (or love) are not the same thing. I would be worried that I simply didn't like her - she could be a completely feckless woman with another unplanned 5 kids for all I know. A bit extreme reaction perhaps. I know this inspires a lot of emotion in people and this view may not be liked, but at the end of the day I have a very strong belief in nurture rather than nature. If I met my biological mother, she would not be my mother - the people who parented me are my mum and dad.
From my own experience and the five or six close discussions I have had with other adoptees, the struggle to trace parents is often less about having a relationship and more about knowing about yourself, where you have come from, who you look like - a sense of identity.
I was very lucky that my parents fostered and encouraged that sense of identity - incorporating adoption. If I can just hijack the thread for a personal plea - please can adoptive parents do the same for their kids. It doesn't weaken your relationship, it shows how strong it can be.
For jofeb04, as I say, a brave thing to do. My only advice personally would be to be honest with your parents that your search for your birth parents is about identity not about criticism of their parenting (and that you are not looking for replacements). And as for your birth family, up to you, but personally I would maintain only a written relationship at the start.
Either way, good luck.
Sorry, long post!