Hey guys, I was at an apartment party on new years eve and met a girl there who was a mutual friend of mine. After a few hours of drinking games and conversation we ended up making out during some mid-night fireworks. She had to leave promptly after and I don't have any of her details (FB, number etc).
I doubt we will see each other that often as I'm not really close with the friend which was mutual with both of us. So my question is how do I move on from here, just add her on fb, or do I try and organise an outing with our mutual friend + her and just game and get details then.

Thanks in advance.

Keep it simple. You already made out, so there's some attraction there. No need for elaborate scenarios about how to meet her using the mutual friend. Message her on Facebook and see where this goes. If she doesn't respond, you have your answer, she made out with you out of NYE enthusiasm and regrets it. Good luck!

Nothing wrong with just adding her or shooting her a message on Facebook. Tell her you had fun on new years eve, be witty and funny and go from there.

Hey guys, thanks for the replies, I did just that, turns out she was already seeing a guy and kept apologising for supposedly 'stringing me on'. I told her it was no big deal and kept talking playful. I'm not really desperate for anything right now so do you guys think it would better if I just kept her as a friend (seeing as she's already a mutual friend), or would it be worth it to try and challenge this mystery man she's already seeing.

Thanks again!