Believe you me - I know how you feel. All of we were skinny when we were that young, and there is nothing wrong with it. You will see that you will get much bigger closer to the age of 19-20. If I were you, I would rather spend the money on good and plentiful food - this will do much more for you. Supplements have all the same stuff from the food, but food is healthier as it has more nutrients, that will help your body get a better foundation.
As per safety reasons, it is perfectly safe to use supplements at this age, since these are all natural, as long as they are high quality of course.