It depends on your budget.

Companies like Nielsen or other international market research companies had offices in these cities and they offered professional research services.

However, many successful teams in the region would build their own research projects in-house. If you are in a budget, you can try free tools like Statista to get a sense of the publishing market. If you want to dive deeper, you can come across with a bunch of Chinese content (e.g. http://ipubl.com/site/gjcb/bg/info/2017/840.html ), which you may need some help; for user interview services, that is not as popular as the west, it may be better if you just hire some part-time helpers to conduct interviews for you.

Marketing channels are highly diverse, there are lots of "agencies" in the region claiming they offer "all-in-one" packages, but they are more focused on executions/ creativity inputs instead of the actual outcome, which should be aware of.

This is a very good question. Fortunately, both Hong Kong and Singapore are very small markets. Thus there is much greater transparency and fewer layers of heirarchy.

I have lived and workedi n Hong Kong for over 2 decades. I also do business with Singapore.

First, is your material in English, Chinese, Both? That will make difference it terms of the market. The local market in Hong Kong will require Chinese language. The higher end of the market and the international schools can work with English. In Singapore, English will work.

I think there are several channels you can pursue.

Since 'youth' tend to go to school, you might want to do an outreach to the schools (probably start with the international schools in both countries and then move on to the better local schools).

There are also local community service organizations that range for Police sponsored youth programs to Rotary and Lions clubs that also have youth programs.

There are many other charitable organizations in each country that could potentially a good channel for your products.

Recreation clubs (Football Club, LRC, Cricket Club, etc) also have youth programs. They might be worth contacting.

I would suggest reaching out to as many of these sources as possible. The ones you contact might not be the right organizations for you, but they can suggest who else might be interested.

Despite the small size of each country, things are still done very much on a word-of-mouth basis. Few good directories of services - not like in the West.

Hope this is of some value. Good luck with your projects.

Should you want to discuss this further, I am available for a phone conversation.