Try posting a message on the internet that say what you already know, and what you'd like to know. There's a good chance someone else is working to solve the same problem, and you'll be able to join forces. You'll get the best results if you post it on a website where the regular readers are also interested in old Hong Kong, family history, or both.
Gwulo.com
You've probably already done this, but if not here are the details.
Facebook works best for people who lived in Hong Kong in the 1950s and later, and who are likely to be remembered by other Facebook users. Here's a list of potential Facebook groups to contact.
Other sites
What other sites have you used to research Hong Kong people, and had good results?