Persuasive speeches do a couple of things.
1 - identify a problem, or potential problem. In this case, your so-called problem is teen pregnancy.
2 - identify what causes the problem. In this case, teen pregnancy is caused by teens having sex without the proper protection.
3 - identify ways to solve the problem. In this case, to solve the problem of teen pregnancy, teens must start using birth control methods of some type, whether it be the pill, the shot, condoms, abstinences, etc.
4 - persuade your audience to change their lifestyle to incorporate 3 into their mindset. In this case, you want to persuade all the teens out there that teen pregnancy is a real risk unless they take the steps described in 3.
Use those bs statistics in the post somebody posted a while ago. That's what your teacher is going to want to here. Make teen pregnancy look like the scourge of earth. You'll do fine