You don't want to see this person again. As yo say you have a lovely life now and that horrible past is well... In the past. Finding that person will bring up the past and to be blunt, what makes you think this person will care? He is either terribly sorry for what he did (unlikely) or hasn't changed at all, in which case would he really care what happened to you?

I don't mean to sound harsh there and I certainly don't want to upset you.

You are looking for closure, I totally understand that. Very different but someone pulled a knife on me, held it to my neck and threatened to kill me a few months ago. For weeks afterwards I wanted nothing more than to tell that cunt I wasn't scared and I am ashamed to say I wanted revenge, to make that man feel the panic he made me feel.

Now I am not saying your end goal is the same as mine, not at all. But the moral of the story is the same, thinking about the events of the past and how you want someone to know how you felt will burn you up inside. But it won't change what happened, and it wont make you feel better.

And even if you do find them and get to say your bit, will it truly aid your closure? Ask yourself why you need this for closure, you are in control of your own closure.

If I was you I would write the letter, read it to your new parenter if you are both comfortable (simply because reading hard words to an actual person is a lot more 'releasing' than reading to no one) get them words and emotions out. And then burn the letter.