Martin Wood, 48, was last seen leaving Dream Boutique Hotel, Petchaburi, by hotel staff at around 5am on December 30.
Martin is 5' 10'' tall, medium build, with thinning light brown hair and blue eyes.
Paul Stevens, a gun repairman from Barnstaple, shared an appeal on social media. He states Martin was his best man at his wedding and has appealed for his safe return home.
Martin is originally from Crediton, but now lives in Exeter. He previously worked at Woods Group and studied at Queen Elizebeth's Community College, Crediton.
An appeal for his safe return has been shared by the Lucie Blackman Trust, which helps share appeals for British citizens missing abroad.
From the UK you can call the Trust with information on 0800 098 8485. Calls are free from landlines but may be charged from mobiles.
From overseas you can call +44800 098 8485 but this will incur costs. Please check before you call.
Formed after the brutal killing in Japan of Lucie Blackman in 2000, The Lucie Blackman Trust exists to support British nationals in crisis overseas.
It provides families with information, liaison, advice and support throughout a missing person's case overseas.