When you're in this setting it is important to let the opposite sex know you are interested in them with body language or conversation. Make eye contact, look at him and smile, it's a sign to him you are interested. He will be more willing to approach you. Men are always scanning a room to see who is making contact with them, who responds to them. It's a lot easier to make contact with men than most women think.
Many women miss a lot of signals.
There are a lot of physical ways to let a person know you are interested. Encourage them - many men want a definite sign. Forget all that if you're interested in someone. Don't avoid looking at people as you do on the street to discourage unwanted attention. Leave your friends briefly and move in the vicinity of the man you are interested in, go to the bathroom but take the long way around and walk about.