Not saying this is the best approach and it won't be a popular opinion, but drugs--particularly alcohol--were key to me breaking out of my shell.
Of course, don't actually do hard drugs without medical supervision. You are more likely to end up worse off. A counter anecdote, a friend of mine who was really extroverted is now pretty shy and nervous in social interactions after suffering a few psychotic episodes during one of our drug binges.
So in short my first reaction to meeting someone wasn't avoidance but instead to interact with them.
Alcohol in particular is a really nasty drug. Psychedelics are something I love to do every now and then, but they're really not for everyone and should be approached with caution.
A small dose of MDMA though. A little goes a long way, not a bad shout if you're open to it.