At 16, you are at a prime age to make huge gains in strength and size -- guys in their late teens / early 20's don't NEED steroids to get big and strong. You need lots of good food, a good workout program, and enough rest to recover from your workouts. Don't underestimate any of these 3; if you leave any of the 3 out, you'll be shortchanging yourself.
There are several guys on this site who do compete in natural bodybuilding competitions (ie, steroid-free and drug-tested to verify that) who can give you a lot of good advice to get started. Welcome to the site, and good luck on your journey!