Should I try to get my friend some help?

My friend has skipped an entire week of school to go drink and smoke pot. He's gotten arrested a few times. He's gotten drunk and stoned on a cruise, and his parents found him muttering gibberish. He's spent $1000 from what he saved up when he was a paper boy, and smoked it all in one month (about 7 grams a day). He's been kicked out of a local mall for smoking in their bathrooms. He's said he was quitting smoking many times, but always went back to it. He's 17, I'm 18. I can't really keep an eye on him so he doesn't fuck up too much since I don't hang out with him enough. Should I recommend him getting professional help?

I was with someone once who didn't tell me he was doing drugs until we had been together half a year. He told me he was smoking pot. I also ended up finding out he was doing a bunch of other things too. I asked him to stop, and he said OK. But he never did. I tried to tell him the stuff was bad for him but he wouldn't listen. Eventually I told him it's either me or the drugs.
He avoided me after that. I couldn't get ahold of him at all. Bumped into him at the mall and he literally ran away. A few months later he comes back and tells me that he's leaving me for someone else. Go figure, it's some girl who doesn't care about his drug habits. :\
The thing is, people who're doing drugs aren't going to stop for anyone but themselves. Just don't bother. It's pointless.