First, due to your age, find out if you will need a work permit. If you are going to accept money for your design services, you will need either a business license or seller's permit. Then, get started by registering on freelance websites that are geared toward creative professionals, such as http://www.allgraphicdesign.com/jobs.

I will forewarn you, graphic design is a competitive field, and you will be up against people with the full Adobe Creative Suite, a design degree, and years of experience. It'll be tough for you to get work. Your best bet is to keep practicing, doing what you're already doing, and start preparing now for a career in graphic design.

If you'd like more links to the top sites freelance graphic artists use, or if you'd like information on choosing the right graphic design school for you, email me anytime.