Feeling Invisible

I feel like I'm invisible. I used to feel like I was the center of attention all of the time, but ever since I have gotten to high school I feel like I have become invisible. My friends are pretty and they can sometimes be guy crazy, but guys also like them and ask them out. No guy ever asks me out and that makes be feel very depressed inside. And it shows on the outside. Like I'm told that I'm pretty, but I don't feel like it. I need help.