Escort - will definitely not be a good choice of word especially when you are a lady asking a male foreign tourist. It would sound like your offering extra service to him.
Try this:
Hello there! I see that you are probably traveling alone here. Do you need a local like me to show you around town? If you would like I can be your guide for the day as I have much free time on my hands. This way I can practice my spoken English with you while you get to see the best places Hong Hong has to offer. What do you think?