Hi.
If you are very popular at school, you may want to be more proactive in talking to guys. If you are pretty and have a lot of friends and people flock around you, guys may be intimidated, thinking, "She would never go out with me!" Show them you're accessible.
However, the most important thing in your situation is to try not to worry so much. Worry will only make it worse. Anxiety tends to send the message that you are desperate, which is one of the surest ways to send guys running in the opposite direction.
Being anxious about it may also motivate you to do things you may regret later just to get a boyfriend. It may also make it more likely that you will settle for a relationship that's not quite right for you because you just want a boyfriend.
I know it seems as though everyone else your age has a boyfriend or has had a boyfriend by now, but that's certainly not true. There are many people, including myself, who found their first boyfriend and had their first kiss much later--I was 21! I certainly don't regret it. I felt a relationship came along when I was ready for it to come along.
Don't worry. I'm not suggesting that it'll take you that long to find one--most of my friends had their first relationships earlier--but in the meantime, continue to be your fabulous self. Hang out with your friends and hold onto that positive attitude. Someone will eventually recognize your glow and want to bask in it.
You can also visit the being single message boards where you'll find other girls going through the same situation as you.
Take care.