The BBC reported that Mr Armstrong had been found alive and well.
Mr Armstrong, from England, had been on a dive master course on Koh Tao since last April, but was due to return to the UK over Christmas.
However, his mother said he had postponed the journey back after “running into trouble” in Bangkok, and was instead due to catch a flight home on January 8.
Mr Armstrong never boarded the flight and had not been heard from since.
Police found that money had been withdrawn from Mr Armstrong's British bank account by someone in Bangkok in mid January.
Tom Armstrong’s father later came to Thailand in order to search for him, in collaboration with Thai authorities. Those authorities announced this morning that Mr Armstrong was “safe and well,” but did not elaborate beyond that description.
The East Anglian Daily Times quoted his mother Helen Armstrong-Bland, saying: “I’m not sure if he is aware of just how much coverage this has had in the media.
“I just want to thank everyone in the Saxmundham community, our close friends and family, and people from all over the world – complete strangers. We wouldn’t have found him without them.”
Tom’s disappearance sparked an international hunt – with an online appeal through social networking website Facebook revealing a potential sighting in the centre of Bangkok.
The sighting came almost three weeks after police revealed that money was withdrawn from his bank account in the city.