My daughter is now 35. Her father is a boy I went to school with and we got heavy after school and I got pregnant. My parents chose to move rather than pay the social price of having me pregnant in high school. My daughter was born and I put up with the shaming but kept my daughter and I managed to complete an education and support myself (I was 27 when I managed to get out on my own). I am doing all right. The guilt I have is that my daughter does not know who her father is, and her father does not know about her. I found him, he is married with a family and appears to be successful and all. I confess to have taken a trip to where he lives and having spied on him. I spied on his wife. I am trying to stay away. I am consume with feelings, some I am sure are guilt others are obsession. I am scared that I will step over the line and do something stupid. I have my life and he has his life, my daughter has hers.
I think you need to be careful with your actions, but your daughter also has a right to know who her father is if she asks. Same with the father.
If your daughter asks about her father, you can tell her you know where he is. She will probably want to know eventually, so in that sense, it's good that you know where he is. And IF that time comes, you will want to notify him BEFORE she goes looking for him, certainly.
But until then, you need to stay away from him. Your daughter will decide when it's time to meet him. Believe me, this is always in the back of her mind. But it has to be her decision.
Have you ever had any therapy? I think it would really be helpful for you to work through the feelings you're having right now. You have every right to be feeling how you're feeling (and I am sure they are very strong emotions), and a therapist can help you figure out the best actions to take (or not to take) in this complicated and confusing situation.
I know you want to tell him he's got another child. And for HER sake. But be careful here and don't take any action until you've gotten the counsel of a professional and neutral third party.