Where did you lose it?

Contact local management of that area and city management in case someone turns it in. Also check Facebook groups and post there to reach a wider audience.

I've heard some cases where someone's wallet was found in a trash can after cash and Octopus card was taken out.

Take proper precautions by contacting bank to cancel all your cards and arrange replacement. If your wallet isn't returned after 2 weeks, arrange to replace your HKID as well.

Please also update your post if you find your wallet.