I'm sure that the US Government does not know where in HK a certain man is at any given minute, if that man even half-heartedly attempts to become invisible. HK is a small, but very densely populated place. It's an arcology, for all practical purposes. There are too many ways to get to places and leave them; there are too many people to get lost among.
If necessary, the Chinese police could have him watched and tracked. Probably they do that. But they are local, they know the place, they have authority to go anywhere, and they can effectively access all the information systems to find out what CCTV cameras saw the man, where he was paying with a credit card, what hotel he is registered in. Can you imagine what kind of a spy network the USA would have to deploy essentially overnight just to track one man? If they could, they would have killed him; it would be technically easier than to follow him everywhere, in the crowd. But they don't know where he is. A man can lay low in HK for as long as he cares to, receiving deliveries from any store right at his apartment, and working remotely over the Internet and a few secure (Tor-like) proxies. (A geek's dream.)
If the feds really wanted to find someone in HK, they could go to the Triad crime families who know where everyone is. They might have to offer something substantial in return, but business is business. If the NSA knows where you and I are now, how can they not know where the most wanted person on their list is right now?
Interpol - Global Police - has access in HOng Kong.
