Coming from a girl; it would be creepy! I wouldn't be completely freaked out if it happened to me, but I probably wouldn't say much because 1) that was random and I don't know you, 2) i'm shy as it is. A lot of girls would find it really creepy, in my opinion.
Plus, they might avoid you because they are there to watch a movie rather then talk to strangers, but hey.. you never know, maybe you should explain the situation and why you are talking to them, rather then making it seem like you're at the movies just to talk to random females lol :p
I don't know, whatever you do.. good luck :D