I became a vegetarian at age 13 and vegan at 16, so I understand the isolation you are feeling. My friends and family all thought that I was weird and my mother was convinced that I was going through a phase but was too stubborn to admit it.
I think that there are a lot more options for socializing with people who have made similar lifestyle choices or with whom you have something else in common when you are older. I recall going to a Mensa meeting when I was about 20 thinking that I'd meet other bright people with whom I could talk about interesting topics only to find that I was the only one there under age 50 - lol! I, obviously, didn't keep attending.
I'm in my mid-30s now and do find that I can go to vegetarian society, or other types of meetings and find people who are close to my age or that age no longer matters now, but as a teen you are probably not wanting support from people your parents' age!
A couple of places you may want to check to find support from people in your age range:
Vegetarian teen online magazine
Peta's kids website