Kids with ADHD who are on medication are many times not hungry until after the meds wear off, and then they are very, very hungry because they have not eaten all day. http://www.additudemag.com/adhd/article/957.html
If your son is overly heavy, then you have cause to worry for him, but if his weight is in the normal range- then he apparently needs the extra food.
You can try providing extra protein content in his dinners or around bed time. Simply get the high protein drinks like Ensure. The extra protein will help with his hunger. Also don't have "empty" sugar heavy foods in the house.
More info that may be helpful can be found in these links.
http://www.additudemag.com/adhd-web/article/750.html
http://www.additudemag.com/adhd/article/11028.html
Hope this helps!
I put stuff in room and I leave snacks out for him but he still eats everything else it don't matter if it's in the fridge or what it is as long as he can eat it he's eating it no matter what
I know it's not what you are hoping but it might be the step needing to be taken to only keep some food available at arms reach. The combination of teenager, boy, adhd, autism.... lots of factors that mean your actions need to be adjusted specifically for the care of your child - and in this case it might mean the extra extemities in keeping the food locked away.
reprimanding clearing isn't working - it's not your son's fault either, nor yours! it makes it harder when no one is wrong, but locking up the food may be the best step until seeking food has passed. :)
good luck!