See dermatologist. Meds- Minoxidil (Rogaine) & Finasteride (Propecia), Surgical - Hair transplant. Eat a nutritious diet to avoid deficiencies. Avoid hairstyles that pull hair tightly. Use gentle shampoo. Avoid hair dryers, permanents or curling irons. Consider use of a wide toothed comb. Consider acupuncture. Genetics plays the biggest factor in balding for most people- you may or may not have success.
Teenage baldness. Teenage baldness is not very common. If you are indeed losing hair at that early age I would recommend that you and your parents set up an appointment with a Dermatologist. You may need to go through your doctor to get that referral.