He's almost certainly crushing up some pills. Probably snorting the powder.
If he has add and takes meds for that, he might be crushing up dexedrine beads and snorting the powder. I used to grind up dexedrine spansules, although I didn't use the aluminum foil. Of course he may also not have add, but he could be getting add meds from his friends. Some kids sell add pills in school.
Just watch to see if he's either gaining or losing weight. If he's eating a lot and gaining weight, he's using painkillers (percocet, vicodin) most likely. If he's losing weight and doesn't eat that much, he's using stimulants (speed pills, like adderall, ritalin, dexedrine.)
i generally wouldn't be concerned until he seems to look sick a lot. You might want to ask what's going on at this point.
Knowing drug users, he's not going to tell anyone what he is doing. The best idea is to either sit and wait a little (don't go to your parents!), or maybe tell his best friend that you have concern for your brother. And maybe his friend can ask him if there's a problem.
I think that may be your best bet. I wouldn't advise telling your parents right away unless you're really worried.
Lemme know how it works out! And he'll get through it. Eventually all drug users have to quit, especially in addiction.