Police are hunting the mystery German boyfriend of a Thai man allegedly gagged and murdered in his apartment in Thailand.

Officers discovered the corpse of Nai Attapan, 39, naked and lying under a bed with a towel crammed into his mouth in the early hours of April 2. His body was bloated and emitted a foul stench, suggesting he had been dead for several days.

Police said they rushed to the four-storey building in 'Sin City' Pattaya after receiving a report at 4 am.

They said Nai's room showed no signs of assault or struggle, though a two-inch-deep wound was found on the right side of his torso, causing his blood to pool onto the floor. His phone was still plugged in and police were unable to unlock it.

Investigators said bowls, dishes, food boxes, and a bag of soup were laid out at his feet, indicating he was about to have a meal. They also collected a fake gun, two suitcases, and a cardboard box from the scene as evidence.

Friends of the suspected murder victim said he had a German boyfriend, who police are now trying to trace.

Police Lieutenant Sakkayaparp Chaidech of the Pattaya City Police Station said: ‘Normally, the victim does not bring anyone to his room.

'His friend told us that he had a German boyfriend, but the friend did not know him personally and did not have any information about him.

‘The police are yet to find details about him, including his name. At this stage, we do not have any suspects as we lack in-depth information. We are gathering evidence and determining the cause of the Thai man's death.

‘When we arrived, the victim's phone was locked, and we did not know the password to access his personal information. We only know that he returned to his room alone after being dropped off by a motorcycle taxi rider.

'We would like to find the German man and speak with him to get more information about the murder.'

The gruesome discovery was made after Nai's concerned friends, unable to reach him for days, paid him a visit at the apartment. They arrived at the entrance only to be met with the overpowering smell of decay. Alarmed, they urged the landlord to open the door and found the gay man's naked corpse.

Nai's friend Seksan, 44, a bar owner in the area, said: 'He was part of the LGBTQ community and had a German boyfriend who supported him financially. Normally, he was a good-natured person, though he could be sharp-tongued at times. He loved to drink at my bar.

'The last time anyone saw him was on the morning of March 29. He had a drink at the bar and went home on a motorcycle taxi. After that, no one could reach him.'

He added that Nai's favourite gold necklace was missing from the room.

Authorities said Nai's body was taken to the Institute of Forensic Medicine for a post-mortem exam. Police were tracking down his German boyfriend.

Former fishing village Pattaya became popular with American troops on 'rest and relaxation' breaks in the 1950s and 1960s when the U.S. military had bases in Thailand while fighting Communism in Vietnam. Rural families are said to have even dressed their sons as women to cash in on the gold rush.

The handful of bars in the coastal town quickly grew and it is now the world's biggest sex holiday destination, with round-the-clock prostitution and drugs - a modern-day Sodom and Gomorrah rife with crime and debauchery.

Government chiefs have attempted to clean up the city but regular violence, depravity and claims of corruption continue to blight its reputation.