@Sean *****
I assume you’ve been back to the bank and made sure they’ve not got it (make sure the person fully understands what you’re asking). Failing that, try the nearest Police Station to the branch. It may have been handed in there. Other than that, check the consulate to make sure it’s not been returned. Last ditch, check all Thailand/BKK-related expat social media sites. People often post ‘found’ posts online in the hope that the owner will see. Good luck mate