Rescue workers discovered his body on the ground below a balcony of the building, reports the Bangkok Post. Authorities reported no immediate signs of disturbance inside the room.
Initial investigations suggest suicide and there were no indications of foul play, police told Reuters. CCTV showed no sign of anybody entering his apartment, where he had lived alone, but his body was sent for an autopsy.
However, police have not ruled out the possibility of foul play pending forensic examinations, a process that could take several months.
The death occurred on Feb 9 but did not initially attract media attention in Pattaya, which has a large expat population, until The Sun newspaper in Britain reported it on Thursday (Feb 19).
Police quoted a Thai friend of Griffiths as saying the Briton had been worried about a lawsuit from his former wife, a Thai national, who accused him of misappropriating £500,000 (B21 million) from a company they jointly managed.
Documents related to the lawsuit were found in his apartment, the police said.
Last year, Mr Griffiths was questioned by police about allegations that he had forged documents in order to sell land and business shares without his former spouse’s knowledge. He denied the accusations at the time and was released following questioning.
Mr Griffiths co-founded ASOS in 2000 alongside Nick Robertson and Andrew Regan. He served in a senior marketing role until 2005, stepping down after four years.
In 2010, he reportedly received £15mn from the sale of shares in the company and realised further gains from additional share disposals in 2013.
Subsequently, he launched legal action against BDO, alleging that he had received incorrect advice regarding tax mitigation strategies linked to the sale of shares. As a result, he said he was required to pay more than £4 million in tax arising from the sale of ASOS shares and another online retail venture he had co-founded.
Mr Griffiths relocated to Thailand around 2007. Following the breakdown of his first marriage, he later married a Thai national and had a son and a daughter. The couple separated several years ago.