When you're a teenager you often feel alone, like nobody understands you -- until you find a girlfriend. Having a girlfriend as a teenager is a fundamental rite of passage and helps you discover who you are. Many people have their first experience with love during high school -- a time when your emotions are at an extreme high. If you want to get a girlfriend as a teenager, you have to be willing to talk to more girls and think outside the box a little.
Participate in school activities and activities outside of school. If you want to be super slick, join clubs or organizations that primarily have girl members. Regardless of whether or not your friends make fun of you for doing something like Drama Club, think of all of the quality time you will have alone with girls. Lack of other guys also means lack of outside competition, which gives you the upper hand.
Talk regularly to the girls who sit next to you in your classes. Make jokes or find an excuse to ask about something related to class. Sparking conversation with girls in your classes will increase the chances of these same girls saying, "hi" to you in the hallways. Considering that high school girls -- not unlike wolves -- travel in packs, when you say, "hi" to girls in the hallway, you also have the opportunity to say, "hi" to their friends.
Make friends with girls who have girlfriends you want to date. It's always easier for guys with lots of female friends to meet girls, primarily because when you have lots of female friends you know more girls. Extending your female network also gives you the opportunity to meet different kinds of girls who may be looking for different qualities in a boyfriend.
Don't act interested in having a girlfriend. It is an unfortunate truth that more often than not, high school girls are more interested in guys who are not interested in them. One of the elements of "high school cool" is not caring about anything, including girls. Act nonchalant and vaguely uninterested when you are talking to a girl you like, but pay just enough attention to her to spark her interest.