Well, when I was about your age I told a classmate how I felt. It went much better than I ever thought, the person I told was very understandable, and said lots of nice very nice things to me. But it wasn't enough. That person couldn't do anything more than comfort words.
Later my parents started to realize that I was not very well (allways in bed, not wanting to do anything...) and my journey started...the journey of going through doctors and psychologists. It was a very though thing to do at the time, specialy because the first time they schedule me an apointment without telling me a thing, so when I realized I was in a mental health professional (not that I dind't already want it).

At the time, and still now, I know there can be many ways to get some help, even without telling or parents. But for me the best way to get it, was to at least give my family some clues about how I was feeling (little by little, and not telling them the all picture). If you think they would support you, they would understand you and they want the best for you (what should to be a condition of being a parent), in my humble opinion I think you should at least tell them something.
I didn't knew what to say too, and specially I couldn't make myself tell them I wanted help, so what I did: start to complaining about little things (my memory isn't working, I can't go to the exam, I will fail, don't be afraid to start crying in front of them...in my case of course) and it worked, very hard and took me a long time, but it worked. Surely not the best way to get things donne easily and quickly.