Funny enough, I'm in pretty much the exact same situation. Except being "shy" isn't holding me back. It's the fact that I really just need a good opportunity to talk to her one-on-one and shit. I went out of my way to go up to her to introduce myself, but that's pretty much it. The fact that she's in a different circle of friends makes it hard for me to even be at the same place with her.
This is what I would suggest:
As your best friend for a hook-up! That's what I did (It's currently pending for my situation though). Ask him/her to invite you to a get-together that involves both your friend and that particular girl. In that way, you can establish yourself within their circle, get more comfortable around her, and start to converse with her.
Once you've gotten a little bit more acquainted with her, wait a couple of days then send her a friend request on facebook (if she hasn't already sent you one). Honestly, I find messaging or adding up someone you like (or anyone for that matter) prior to getting even a bit acquainted with that person to be a little stalker-ish. It's more likely to backfire on you rather than working wonders.
Get comfortable with her. Post something clever on her wall that involves like an inside joke that you or the group shared that night you guys hung out. Have a long conversation with your wall-to-wall or something. Nowadays, this is some of the shit that's pretty much vital due to how much technology has evolved and seeped into our lives. Be thankful for that coz "shy guys" like you can benefit from this. Just remember, avoid looking or sounding creepy or clingy in any way. Play it cool bro.
After that you can work your way to getting her MSN. Chat it up. Eventually, you'll have her on your contact list on your cellphone. Converse. Keep her company! LISTEN to what she says and remember them. Be suave. Make it obvious that you're interested. You'll know early on (if you can decently read people) if she's either interested or NOT at all. Although girls are pretty fucking complicated specimens, so I wouldn't blame you if you misread. Almost every guy in the world has had at least one bad read in their lifetime. Haha
Ask her out if all goes well. Again, be smooth. This is when all the technological, somewhat pseudo bullshit ends and you enter the "real world" phase. Take her out on a date, impress her but be yourself and hopefully you'll get the girl.
As corny as most of these steps may sound, it's an approach that "shy guys" can work with. I can honestly say I actually ended up dating a girl doing the whole "facebook wall-to-wall---> MSN ---> text marathons ---> ask out--> actual date ---> relationship" method. Which should be a pretty common one I might add.
Otherwise, just skip everything and man up. Just talk to her! Go out of your way and do something. Girls like that because it's becoming less and less common for just a straight up personal "can I have your number?" thing. If you wait too long, she might end up being unavailable and taken. You wouldn't want that. The regret is more painful sitting around doing nothing rather than doing something and being shot down. Life is shit my friend, but sometimes you can luck out and get rewarded big time
Good luck OP
