Today, I thought I'd tell you about TeenInk, in case you've never heard of it.
As you probably gleaned from the title, only teens can submit their work there. TeenInk puts up articles, poems, stories, you name it, onto their website. They even select some of the pieces to go into their monthly magazine; they'll print those works for free. Others can comment on your work and offer feedback, and it's a great way to start making little networks with others your age. Registration is free, by the way.
Check it out. http://www.teenink.com/
I think you'll like it.