Nathan Hansford, who has worked in Bangkok for 10 years as an international contractor specialising in public finance and capital market development, has not been in contact with family and friends since Christmas.

His family said he regularly travelled internationally for work assignments but had always kept in regular contact with his Australian family and friends throughout his travels.

They said his mobile phone had been disconnected and he had not been using his email or social media accounts.

In a statement, the family said it "hopes that Nathan is oblivious to a search across Thailand for him and that he is ‘lying on a beach taking a holiday’."

"This situation is out of character and the family holds grave concerns for his whereabouts," they said.

Mr Hansford was last seen leaving his home in the gated suburb of Thungkru on January 31 to travel in a taxi to Mo Chit in central Bangkok.

Family members plan to fly to Bangkok on Tuesday to help local authorities search for Mr Hansford.

"Thai and Australian authorities have been very helpful," the family said.

Mr Hansford is married to a Thai woman and lived in Canberra before moving to Thailand in 2004. His parents and brother still live in Canberra.

Family members are calling for anyone who has information about Mr Hansford to contact the authorities.

A social media campaign to locate Mr Hansford has been led by the partner of Mr Hansford's brother Hamish, Tara Cheyne, who tweets at @In_The_Taratory.