Background
About 15 years ago I used to frequent a particular online forum and had made many friends there. I still have contacts for most of these friends. One friend in particular though, despite being us being very close, was never allowed to give out contact info to people she met online, so we only chatted in the forum. After a few years, life happened and I ended up moving away from that forum to other things and we lost contact.
Recently, I was remembering old times and decided to go back to the forum for a nostalgia trip. This reminded me of my old friend I hadn't talked to in about 12 years, and I wondered what she'd been up to, but she hasn't been on the forum in years so there's no way to contact her through there.
I wanted to see if I could track my friend down. In short, I used a combination of saved post history on the site and a publicly accessible image hosting account with identifying information, particularly the school they attended, to find her on Facebook. Her online persona and real life were pretty well separated, and I was only able to find her because I have practice with finding security vulnerabilities.
Despite us being close friends from a long time ago, I don't know if she ever intended for me to know her true identity. I don't know if she's kept in contact with any other friends from the site, we didn't have any mutual friends that I was close enough to that I could go through to confirm this.
I didn't do try to find her with the intent of contacting her, I just wanted to see if I could. It actually took a lot of effort, if I had to do this just to get back in contact, I probably wouldn't consider it worth it. I have done similar things in the past, of identifying people based on their online presence, but have never contacted anyone afterwards.
Problem
Now that I have a way to contact my close friend from so many years ago, I'm tempted to do it. The idea to find her in the first place came from wondering what she's been up to. I would like to catch up and possibly maintain an online friendship (assuming it was mutual). I want to explicitly state that there are no romantic feelings/intentions here, our relationship has always been purely platonic and I have no interest in changing that. That being said, I'm a male and she's a female and we are just about the same age.
I've considered just reaching out and asking if she is $username
from the forum. She may or may not recognize me immediately, as my first name and hometown are public on Facebook and known to her, but I also have a very common name and currently don't live in the same city/state I did then. If I mention the forum, it's likely she'd recognize me; if I just sent a friend request, I'd guess maybe not but it's possible.
Regardless of my approach, I think one of the first questions she would ask is "how did you find me?", and this is where I'm stuck. The methods used can easily be considered stalker-ish, and though I know I'm not trying to be a stalker, she obviously doesn't and the facts are pretty damning.
My question is, is there a way to contact my friend, explain how I found her and then assure her I just want to catch up, without being seen by her as creepy or a stalker?