Please note that to do all this effectively it will have to be done in Japanese, except no5, for which any way is fine.
1. Check with the local collection centers. The bike might have been removed by the orderlies. Contact numbers for within Tokyo: http://stolen.concents.net/blog/?page_id=202
Apparently it takes them a couple of days to file a bike, so check first if there was a cleanup in the area, then which holding they bikes went to and then bug them for a while. For central Tokyo the Shibaura collection space seems to be well used: 03-3452-3710
2. Social Media. Get the info out there quick. Twitter and Facebook public. @Cycle_Search has more than 2000 followers. Sending it to @stolen_bikes will likewise distribute the info further.
3. Register with theft trackers. http://www.cycle-search.info/ and http://stolen.concents.net/bbs/
This will also give you an indication about theft activity in the area, so the likelihood it might have been an organised hit.
4. Police. Go to the police even it they do not seem helpful. If it happened in Tokyo, any police box will do. Even if the bike was not registered (防犯登録証), as long as you have a frame number (車体番号) they cannot turn you away. Prepare all info, so the bike can be identified if found. They will also prepare a theft certificate, that might be necessary for insurance claims.
5. Second-hand shops. The bigger shops will accept information about stolen bikes in advance and have special email for that. I would still also email the smaller ones, just in case. Although they have to take ID from all sellers, what there protocols are when they identify a stolen bike, I don't know.
3. Set up alerts on auction sites. Yahoo, rakuten auctions and bidders in Japan.
4. Insurance. If at home, home insurance covers it. If at a paid parking space, they have liability. Theft insurance might cover it.
5. Take the law into your own hands. If you have some leads, follow up. Don't expect the police to do anything proactively. If you found the culprits, smash their heads in, but don't do anything irresponsible.
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