I'm so shy around new people?

Basically, fallen out with my two bestest friends. And all my other friends are going different colleges and sixth forms. Anyway, I want a whole bunch of new friends. But I'm so shy. I just don't know what to say in conversations. For example, the other day, I was with one of my other friends, and she was with 4 different girls who I've never spoken to before, but I know who they were. I couldn't get a word out. I just didn't know what to say or how to join in the conversation. I just want new friends.