She's prettier

I was introduced to this group of friends in a bar by a mutual friend. There was this really attractive looking girl from across the table that caught my eye. I maintained eye contact and she broke it off first with a smile.

Now there's this other girl sitting beside me who also was clearly cute, but not as attractive as the first. I took advantage of her proximity and gamed her. To the point where I held her hand for a few minutes before she let go. I didn't know if my first target saw what happened. But the night ended with me establishing a stronger connection with the second girl than the first. And I kinda regret it.

The first one was prettier.

I added both of them in facebook. Now I want to ask this prettier girl out. What's the best way to go about it? I only got the second girl's number.

A simple, "Hey, you're the girl from the bar the other night right?"

Continue to get to know her, make her interested in you. Flirt. Number Close.

So I can continue flirting with her online? On facebook? She actually was asking me a few trivial questions that night, so I can tell she has a bit of interest. I just don't know if I can see her again to nonverbally flirt with her, which works for me.

Is it ok to ask her out on facebook?

I would Number Close on facebook and then lead it off with some texting game. From there, ask her out.
That is just what personally works best with me.

My sister's friend (She is 27 and I am 25, but I am known by my sister's friends as hot and dreamy so it works to my advantage) was recently asking me questions on how casual sex worked. She was quite intrigued by what I had to say (this was at a get together at my sister's house). Over the past 2 years, I saw this girl maybe 3 times at just random get togethers. When I got home, I decided to facebook request her. I chatted her up on that chat thing (which I like to call creepy chat) and we got to talking about hanging out. It was a back and forth kind of thing basically going as follows:
HER: We should hang out sometime outside of one of your sister's get togethers.
ME: Yeah, I agree. We could get drunk and do things we normally wouldn't do, which isn't much to me.
HER: Lol. I agree, you're probably crazy fun.
ME: That I am. Well he is my number XXX-XXX-XXXX. Text me sometime. I'll ttyl, gotta go to bed.

Conversation ended. She hit me up a few days later.
What I tend to do is build that rapport and connection that they want to see me and hang out. I make myself seem a lot of fun, which I am, and then I end the conversation on my term. If the girl doesn't want to text me, fine. She won't and that's her loss (I am not cocky, just confident and I do not sweat the small stuff as no man should). Also, me ending the conversation will either lead to 1 of 3 things.
1) She will text me later (case point in my example)
2) She will reply, well here is my number .... (In which this case, it's also a win because you get her digits)
3) or she will just not text you and that's the end of it.

You have nothing to lose but a little bit of time, but what you will gain is experience.