White Tiger has a good handle on it.
Its only been 24 hours, not to sound insensitive but that's a little soon to be panicking, unless this person has a history of vanishing before, or there's a reason to be concerned. I once vanished in Germany for 5 days freaking out my family, but the girl I found was cute and she wanted to go hiking.
Under no circumstances get on a plane and fly over until you know more. you will be out of communications for a long stretch of time, and you don't know where your going.
Calling the Consulate is a strong idea, because it puts the person on their radar, and they have contacts with local police, and know the language and customs so they might be able to initiate a wellness check.
If you have his airbnb user name, you could attempt a log in and contact the host. I don't think you can get much out of AirBnb emergency services.
You need to report the missing person to your local police and foreign police. You can also report the missing person to the emergency watch and respond centre.
https://travel.gc.ca/assistance/emergency-assistance
You'll need the person's usual information, name, height weight, identifying marks, a recent photo their passport number etc.
You can also try the international redcross
But 24 H is too soon.
Stick by your phone and your computer. Japan is not like Brazil, where Kidnapping tourists is a pokeman type game for gangs.