Im a decent looking guy, take care of myself and dress cheap but smart, I used to have simmilar problems so i feel for you,
The simple thing is, you need to get out of your comfort zone and take some emotional risks.

you have to go out on a limb a bit and be a bit more social.

This is really sad, but i read up on some internet site about dating tips, and the most important thing i learned was about confidence and approaching people.

Your insecure, so start small, ask random good looking strangers in the street if they know what time it is, then move along, and ask again.
If your out drinking and you see an interesting looking drink/food, go over to the table and ask what the drink/food is, tell the people that you are thinking of getting "what ever it is" and you are curious.

you will soon realise that people are hopelessly social, and are happy to talk to you when approached in the right way.

these small confidence builders will help you a lot.
you might get the odd funny look, but ignore it, and carry on....