I agree with what everyone is saying about confidence. People who are confident give off an energy that attracts people, male and female. It's true that some men will ignore women above a certain weight (or women of a certain race, or women who dress a certain way, or women who have bad teeth, etc. etc.), but it's also true that men are just as different from each other as women are! There are men who love larger women, and there are plenty of men who sincerely don't care if their SO's are fat or thin. Doesn't seem like that on TV, but it's true.
Obviously we're all here because we have weight concerns, but there are other ways to make yourself feel more confident! A new haircut can help. Really learning how to put on makeup and dress for your body type will help too. There are a lot of guides online and videos on youtube if you want help with this. The ladies at makeup counters can give you free advice too, but beware--sometimes they have very distinct styles that may not be your personal style.
I used to be painfully shy as a child, but I'm now incredibly sociable! I didn't "grow out of it." I had to make a conscious effort to change. It's hard and scary at first, but you just have to put yourself out there. Start speaking up in social situations, especially situations that aren't romantically charged. Once making conversation with strangers is easy, it becomes much easier to pick up conversations with men you're actually interested in.
All that aside, the best piece of advice about confidence is this:
Fake it till you make it.
Seriously. Even if you don't feel confident, pretend that you do. Next time you go out, just put on a confident persona. Eventually, you'll realize that this "fake" confidence isn't fake after all. It'll become a part of you.
Don't delay. Life is waiting.