By going to "Books & people" and selecting "Browse members", it shows that Hong Kong has 256 registered members. It's likely that some of these aren't active, though. When you have found Hong Kong under "Browse members", you can click on "Hong Kong" to get up this list: http://www.bookcrossing.com/---/7/ Then select a region to see the members in that region.
Welcome to Hong Kong! Are you studying or teaching at CUHK? I was a student there!
The BC group in Hong Kong is rather small, though there are activities similar to BC and Little Free Library in different locations. The BC group does meet occasionally - like once every year or two - over tea or dinner. We also have a WhatsApp group too, you can pm me your phone number and I'll add you.