Force yourself, and jump in. Really, once you're IN IT it becomes a lot easier.
I find that when I had a really social day where I interacted with lots of different people, was the center of attention, etc. Well, after that I'm really not much anxious at all anymore. It's like "well, it is not THAT bad after all"
But when you avoid you make your problem even more real to your brain.
You can start by talking anonymously in chat rooms. If it gets too tense just log off and thank yourself for at least making a step forward