Tom Armstrong, 22, of Suffolk, disappeared after finishing a dive master course at Koh Tao earlier this month, as we reported here.
He was supposed to leave Thailand for home on Jan 8, but never showed up in Britain.
Authorities in Britain said they believed Mr Armstrong was still in Thailand, but are increasingly concerned for his welfare, according to an online report by the East Anglican Daily Times.
Police found that money had been withdrawn from Mr Armstrong's British bank account by someone in Bangkok a week ago.
It quoted a local policeman, detective chief inspector Neil Luckett, as saying police "remain concerned about his welfare and we are urging anyone with information about Tom, in the UK or Thailand, to come forward.
“If Tom is reading this I would urge him to contact us and let us know he is safe,” the policeman added."
The newspaper quoted his mother as saying Mr Armstrong kept in regular touch after he arrived in Thailand last April for the diving course, but has not been in contact since Jan 8.
View the original Bangkok Post story here.