A statement from his family said he was involved in motor vehicle accident and suffered from amnesia.
''It is time for us to focus on helping Nathan in his recovery,'' the statement said.
Mr Hansford, 36, from Canberra has lived in Bangkok for 10 years and had worked in countries including Cambodia, East Timor and Iraq.
Mr Hansford, an international contractor specialising in public finance and capital market development, had 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.
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.
He is married to a Thai woman and lived in Canberra before moving to Thailand in 2004. His parents and brother still live in Canberra.