Teenagers: A group of mostly rebellious youth who are turning into adults, and want to act more like adults so that their parents will treat them with more respect.
Sex: A forbidden act that is only available to adults, feels quite amazing, and is very risky considering all the consequences that come with committing such an act.
See a trend?
Also, some teenagers just do it as a 'fight the power' sort of thing. It's a really weak way of doing that sort of thing, but then again, most teenagers aren't exactly the brightest bunch in the world. If you're being chaste until you find someone you love, then that's fine and dandy, but a big gamble. Very rarely, and I mean very rarely will you find someone you want to be with for the rest of your life, or even for the next week or so. There's nothing wrong with waiting for it to happen, but honestly, you're better off just finding someone you like, like a friend or someone you think is a great person, and doing something sexual with them if they're of like mind. Sex for love is great, but it's sex for just the simple enjoyment of the act, that is one of the things that sets us apart from a more animalistic nature.
Now, I'm not saying go out and get laid with the nearest wench you can find, no. I'm saying don't hold yourself back if you've got the urge/want and so does your partner. You only have X amount of years of sexual virility. Don't waste them.