Yes you should tell someone, and it may not require all that.
You may just need to supplement your diet or go to a dr. and get some medicine.
I was terribly depressed a year ago and was prescribed Prozac. It really helped and costed only about $8 a month (generic), so don't let yourself get all overwhelmed.
You can get help.. affordable help. Search online for motivational sites or go to a bookstore and look through the self help section until you find something that sounds like it's speaking to you. It is hard being a teenager, your hormones are out of control and you're trying to find your place in life but remember... this too shall pass.
Trust me... if you think your family is stressed and burdened now... a missing or dead family member is not going to make their life better.
You need to find a purpose, something that makes you feel good about yourself. Please don't give up.. I promise it will get better. I am living proof!!