Abilify can activate kids or sedate them. I haven't really heard many good things about it, but that's not universal experience either. It is also an antipsychotic, not a mood stabilizer, although sometimes they are used to try to stabilize moods (with various results). Now if you add Abilify to an antidepressant, they SAY that it can make the antidepressant more effective. Perhaps it is the Abilify added to the Zoloft that is making him act manic. The medications game, which I've played myself, is very hit or miss and requires a long time before getting the right combination. And, of course, kids grow so fast. It's harder than medicating adults. Hang in there.
As for the can, I would assume he has already tried street drugs. I know it's not what you want to hear, but my daughter started at 12 and she didn't have a job either. Kids share the pot. They don't make their friends buy it. Any time she wanted drugs, she got them and we cut off all of her money the minute we found out she was smoking cigarettes (this was even before we knew she was doing drugs...she still got cigarettes by the way). My daughter, at first, was very careful not to have drugs around the house. She got more careless as she got older. And no child will confess to using drugs to the full extent that he/she does. My daughter said she "tried pot but didn't like it and I get sick when I drink." Now that she is 26 and clean for eight years, she told me the full extent of her drug abuse AND drinking and it is appalling. We are lucky she's not dead. I'm not saying you should panic, but what you found was a big red flag for drug use. Fourteen year olds can find drugs very easily and they can be deceptively great at lying while staring you straight in the eyes and melting your heart. In truth, a high percentage of depressed people self-medicate, but the drugs usually make it worse in the long run.
Good luck to you and your child. I hope it works out and he's not using drugs.