You should be optimistic about it. Because I was once like you. Now I talk so well with people, especially those I've never met before. 2 things that made me come out of my shell: acting classes. I went to many but they didn't change me that way. But in the age of 16 I joined an acting class that was very good for me and the funnest I've ever been in. And of course we needed to act on stage, and you know what? My self-esteem was improved in like 100%. I don't know if that wouold work with everyone. Because I also had a friend who went to acting class with me and her self-esteem went worse. But it really helped me.
The second thing that helped me, was when I started working at the supermarket. I just had to talk to customers, to sell them things, and sometimes we would have a conversation. So I learned how to talk to people.
You're too shy because you don't have enough self-esteem right? I'm sure you can find ways to work this out. Takes practice, and interaction with people. It wouldn't help you if you hide from people. Start a good conversation with them. Ask them questions about them and then tell them about yourself on the subject you're talking about. Like: "I love cheese". Then you say: "I love cheese as well, I love cheddar. What kind of cheese do you like?" This way you show interest and also make people know you better.
You can also find a common thing. Say Buffy. I'm sure you have an opinion about many aspects of Buffy, so there could be a debate with another Buffy lover. I don't totally agree with your friend. You need to take your time and find your own way. If you force yourself people would notice the fake you. And you need to be real. And stay away from those who hurt you. They bring you down, and you need to find a way to bring yourself up. Be the lovely person I know you are and don't think you should be like everybody else. Let them come to you. Slowly you'll start opening up to people and they will want to be around you. People don't really get along with other people who don't talk, who don't interact. You need to put yourself in and be equal with them. Takes time, but you'll come out of your shell.