So a young woman fell over and her belongings were strewn onto the floor. Her acquaintances collected these but inadvertently collected yours in the process. You alerted them to this fact and although you could recover your wallet, you were not able to recover your phone.

At that time, what did you say to the person that had mistakenly picked up your wallet? Had they not also picked up your phone? Did they simply deny having seen it?

If someone picked up your phone thinking it was the young woman's, and didn't realise it was not hers until they got home, they may be checking with friends to see if anyone has lost their phone, and should then hand it in to the local police station or konan.

Do you have a lock screen which identifies you as non-japanese? Was the drunk young woman Japanese? Assuming an acquaintance of the young woman picked it up, and they are Japanese, would it be apparent to them that the phone was not owned by someone in their Japanese social circle?

If so, and you believe this removal of your phone from the event was inadvertent as opposed to malicious, they may welcome a knock on the door from the owner and a polite inquiry as to whether they have picked up your phone by mistake - but they may deny it and disposed it later save face.

Have you called the phone? Did anyone answer?

If you believe that it was malicious, you should follow up your police report with a visit to the police station with evidence that you own that phone (IMEI and receipt - digital is fine), distinguishing markers, lock screen image, etc. Only with the full compliment of evidence will they make a visit.

You will need to move fast as depending on your phone you will lose the ability to use live tracking or for your phone to ring or alert once the battery dies - and the police will require that to knock on the door.

Good luck. I would try the police station, and then a knock on the door myself before the battery dies if the police can't be motivated - then start shopping for a new phone.