Shane Marsden, 28, from Gloucester, has not been in contact with his family since Tuesday.
Gloucestershire Police said they were working with Interpol to try and find him.
Mr Marsden is believed to be in Thailand after travelling there from New Zealand.
Police are asking anyone who has been in contact with him since Tuesday or with any knowledge about his disappearance to call 101.
Police are trying to track down a tourist who has gone missing in Thailand.