Starting IM Conversations

This is something I have had a problem with for some time, but I think it's slightly worse than usual at the moment, so I wanted to ask if anyone else experienced this:

While I am often capable of seeming almost extrovert online, I have real difficulty bringing myself to actually start instant messaging conversations with people, e.g. on MSN. Even people who I have been talking to for over a year who are quite close contacts (I am hesitant to say "friend", since I never see these people IRL anymore) - once they start a conversation I'm usually ok, but I can never start it myself. I think I have some unshakeable internal conviction that they just don't want to talk to me, and that if I start a conversation I will just be bothering them.

Is anyone else like this, or am I alone in this particular weirdness?