What to Do If You Lose Something at the Tokyo Metro
It's one thing to lose your valuables, but it's an entirely different matter to lose them in another country. If you forget or lose something in any of the Tokyo Metro train lines (this includes the Ginza Line, Marunouchi Line, Hibiya Line, Tozai Line, Chiyoda Line, Yurakucho Line, Hanzomon Line, Namboku Line, and Fukutoshin Line), and the day has not yet ended, head over to the Lost & Found Center at the nearest station. Look for a signboard like the one shown in the photo above.
Lost and forgotten items that are not retrieved on the same day are held for up to four days (beginning the next day) at the Lost & Found Center at Iidabashi Station. Call 03-5227-5741 or visit the center in person. This is the Lost & Found Center inside the ticket gate of Iidabashi station.
There is also a Lost & Found Center outside the ticket gate. On the fifth day after a lost item is handed in, it gets transferred to the Tokyo Metropolitan Police Lost & Found Center. Tokyo Metro has also launched an online Lost Property Inquiry Form system, so you can give this a try, too.
If you lose something while riding a train belonging to another railway company, the first thing you should do is to telephone the company whose train you think you lost the item in, and take it from there.