I don't need to read words to be able to get the context, you know. Some of us put down the books, go into the field and gain real life experience. I don't need to read some copy pasted, or studied walls of text in order to see where you are with your game when you ask "I met friends of friends at a party and added each other on facebook, should I hit on them online?"
If your social dynamics level and social proof is at the level your post suggests in subtext: No. You have to be 100% SURE, ABSOLUTELY CERTAIN, GETTING LOTS OF IOIS AND EYE CONTACT AND KINO from her so you can be sure you have actually attracted her and she won't categorize you as a creep and go tell her friends and the whole social circle that you are hitting on her on Facebook.
Attraction between a male and a female is not like visible communication. It is a sub-communication. It's either ON or NOT. And you don't have to ask us if it's "ok" to hit on her. You either "know" she is attracted to you, or you couldn't attract her at all. Do you understand this? There is the TCP connection established between two hosts, or not. If you were able to attract her within the few minutes you interacted with her and she had an opinion of you: you wouldn't need to come here and ask if it's ok to try her on Facebook later. If you interact with a woman long enough for her to form an opinion about you; and she gets attracted to you: there is nothing she can do to change that. It's not a choice. It's a subconscious biological mechanism. But if you interact with a woman long enough for her to form an opinion about you; and she DOESN'T GET attracted to you: there is nothing you or she can do to change it. No convincing, no trying other lines or routines on facebook is going to convince her to feel otherwise.
Was she attracted? Tell her on facebook to meet you tomorrow for netflix and chill. She won't have much of a choice.
You don't know? Don't do anything, or you risk alienating your friends and your social circle and appearing desperate. Appearing desperate in a group with girls is the equivalent of social suicide. Better find a new group of friends at that point. (Same with work environment. No moves unless you attract her without giving her IOIs)