Food. If you don't eat enough, not even roids will make you grow.
What use is a puny low carb protein shake when you eat chips & cake for dinner?
Once you get food handled (eating 6 times a day with 1 gram of protein /pound of body weight) start thinking of sups.
Best sups are:
shakes: they make your life easier, you can take 40 grams of protein & 700 calories in 1 minute. Also, you can carry it around.
creatine: it gives you more pumped muscles, makes you gain some weight (water though) & gives a little strenght boosts.
Useful if you can take it nonstop, cause you lose all it's effects after a couple of weeks of not taking it.
multivitamins: useful to make sure you got all the vits & minerals your body needs.