Don't worry, this TB/coin is probably NOT missing...
Many geocachers that visit Amsterdam do a few caches, but wait until they get home before they log. This can sometimes take weeks!
I generally wait about 4 weeks, and then mark TBs/coins as missing to remove them from the cache-page (to keep it a bit up-to-date). When the cacher that took the TB/coin finally logs it everything will be back in place again.
Kind regards,
Martijn (DopamineNL, CO of Amsterdam Chinatown)