I went to a frat party for my sisters b-day last night...?

and there were about 5 girls among 20 + guys, my sister introduced me to everyone about 5 times, but I didnt really talk to anybody while I was there, I just followed my sister around and listened to other peoples conversations, There were several guys that were goodlooking and that I should of made conversations with, but every time I started to say something I just bit my tongue. how do I come out of my shell in a social setting like that.