Lost and found station in Tokyo metro

On a family trip to Japan and Tokyo, I stupidly forgot my bagpack in the train at Tokyo station. The train was heading to Shinjuku. There was our 5 passports plus 50,000 Yen and 7000 RMB in cash! I reacted quickly and so did the platform staff at Tokyo station. They ran me to the lost and found office. No English speaking, but images and simple words were enough to be understood. 20 mn later, we had a call from the lost and found station at Shinjuku station, they had sent someone to look for our bagpack and it was waiting for us there. I am so gratefull that I would like to send a thank you email to the staff at Tokyo station. Can someone indicate an email address where to send our thank you email. We were impressed with the efficiency of the Japanese staff, they were professional, helpful and very polite.

Chris,

You can email Tokyo Metro by clicking the blue icon below, but the directions are in Japanese.
http://www.tokyometro.jp/contact/goiken/index.html

So instead, you can try writing snail mail to;

Tokyo Metro Okyakusama Center
Tokyo, JAPAN 110-8614

Please make sure it is Tokyo Metro Co. that you have in mind, because JR East Railway Co. also runs trains between Tokyo and Shinjuku. If it was the Marunouchi Line (red circle mark) that mainly runs underground, it's Tokyo Metro. If it was either the Chuo or Sobu Line that mainly runs over the ground, it's likely to be JR which has a different address.