Just grab one of the guys and say, "hey help me out man, the girl with the gold ear rings, where do I know her from? Does she work at (random employer) / go to (name of local college)? When he answers, just ask "is she with anyone?"

Then say, ok, I'll just grab my drink and I'll come and say hi in a minute.

Then he'll tell the girl that you think you know her and that you're coming over to say hi.

When you get there, speak to the whole group "so is this a works night out then? what's your plans for the night / where are you all heading next? etc

Then say to the girl anything to make a connection. "Do you have a sister called Sara?" Or whatever, and away you go!