May be tough to do at your age (as you are under 18). Your best bet is to audition for plays in your and other local high schools. You may also want to audition at the local community college. For more professional work, check out www.indieclub.com and check out your local branch. Sometimes SAG (Screen Actors Guild) knows about non-paying work in indie films and you check your local person or if you can't find one - start with the one in Dallas - Linda Dowell at 972-361-8185.
Joel