tl;dr When I'm in a group that I don't know very well and people are talking to each other, I just sit or stand there quietly.

It goes like this: When I'm with a group of people and I don't know some of them very well, I kind of freeze up. I'm very talkative with my friends or if I'm talking one to one with a stranger. But when I'm in a group that I don't know very well and people are talking to each other, I just sit or stand there quietly. I feel like I'm losing a lot of opportunities because of this. Is there anybody with the same problem as me who has fixed it?