How to start a conversation with someone in a group?

ok so, I go to this awesome youth group, great people, very nice and someone is always talking but it's never me.. I'm a girl and there are a couple guys I like but I can't ever start a conversation with anyone! If I stand by somebody it's ALWAYS awkward 'cause they try to talk to me but all that really comes out of my mouth is a yes or no.. Or more casual like a yeah or nah.. Anyway i'm very shy as you can tell, but i've kinda ben using "it's always more like a group talk than a one on one thing" but all the other boys and girls are talking to each other like 4 girls are talking and maybe 6 feet away are a couple of guys talking.. It is a group talk like thing but also a one on one.. I can think of so many things to talk about but when I try to say them somebody else might be talking or I just completely forgot them! And tips?...