I'm a very, very shy person too (I think a lot of Smogoners are), but I have many friends, and a big social life. I achieved this in the past few years using a few 'techniques' that I mention below.
With personalities like ours though, we do have to approach socializing differently.
Firstly, you need to stick to your current friends. Make sure you're really close, and that will mean that you will always have them, if all else fails.
Secondly, use your current friends to make new friends. Your friends will have friends that you don't know. Try to organize small gatherings with a few of your friends and their friends. Make sure there's under 10 people, so that you won't be left out of the group, and so that there'll always be someone to talk to. After a few occasions, you may be close enough to these friends to be able to meet up with them without your connection. Eventually you'll have a big 'web' of people's social lives intertwined with your own. It's pretty difficult to make new friends on your own.
Also, the use of social networking websites such as Facebook help to get yourself involved with others. You can find out about people before you decide to meet them, so you can get some expectations about what they'll be like before you meet them, and you can also find out who both of you know.
Two important things to do though are be nice, yet fun, and NEVER gossip. Gossiping may seem like an easy way to make conversation, but it's just darn cruel and will not provide a very comfortable and laid-back atmosphere for you. If you happen to be with someone who likes gossiping excessively, they're not worth the effort to make good friends with.
Basically, don't try to make new friends on your own. Always use your closest friends to help you, and hopefully you can talk with them about your problems. Also, be yourself when you're with them. Don't try and act cool, as they'll notice and be annoyed. Also, be relaxed when you're around new people. Having your friends around helps, but just remember that people aren't going to remember anything stupid that you do after a couple of hours, and if they're nice, they probably won't care either. And finally, if people tease you, and try to lower your self-esteem, you should distance yourself away from them. It'll do you little good to try to still be friends with them.