It took a lot of guts for you to post a thread topic like this. Perhaps you aren't so introverted after all.
I can present some insight from my own personal experience. I am an introvert as well, but over the last 5-7 years, I have developed skills to be more socially adept. Furthermore, I have naturally developed these skills thanks to the social activity on the Internet. Once I developed those skills online (in chat rooms, instant messaging and forums), I transferred them slowly to non-virtual life. Slowly, I found that I could be as funny, insightful or intelligent as I was in the virtual life. Eventually, I happen to cut off most connections from the virtual world and spent most time in the non-virtual world. These days I am spending a bit more time in the virtual world than I recently have. There has been a significant lack of intellectual simulation in non-virtual life and I think I require it. Joining this forum would help me with that. But I digress.
What I can suggest to you is to involve yourself in conversations online. Develop a character for yourself that is true to you. Don't fake it. When you write something, ask yourself, if that is really you or just someone you are trying to project to fit in. If you don't fit in to some online group, don't worry about it! Go somewhere else. No feelings will be hurt! You don't have to worry about that sort of stuff until you go to the non-virtual life.