I am an international student studying in Hong Kong, call me Michael if you'd like. I turn 17 in May and I understand your situation quite a lot. I got a job last summer at a company that sells medical equipment to hospitals and clinics, however, after a week of working there, I didn't fit into the work environment due to the lack of Cantonese I could speak.
Finding a job here that only requires English as a language medium is quite difficult. Bars and clubs are certainly out of the question for us as it is illegal, however, I believe some restaurants like Fat Angelo's, and Krispy Kreme are willing to hire teenagers, especially during the daytimes (at lunch hour) where most of the youth community are at school.
Otherwise, you could try to help out at an international primary school. Beacon Hill, Kowloon Junior and Clearwater Bay school are all ESF schools and they might be able to find some sort of assistant job suitable for your son.
Other than that, I'm not sure what else there is. English-medium jobs are really hard to find here, and unless you've got qualifications, you can't really do much besides waitering and assisting.
If all fails, maybe going to do some charity work would be good, so you don't waste your time here. I go to Crossroads International (Crossroads Foundation - Home) and I enjoy it very much there when I go there every week.
I wish you luck, waitering isn't really that bad, especially in restaurants like Fat Angelo's. I heard the workers there are very friendly. My e-mail address is if you yourself, want to keep in touch or if your son would like someone to talk to about life in Hong Kong.
I myself, have just sent my brief CV to an employer, looking to hire a part-time showroom assistant. It's only for weekends, as I have school, but I won't know if I get it 'til they send me a reply. So wish me luck too with that. Haha.
That's it from me,