The man was identified by Chalong police as Joshua Steven Weitz, 39.
His body was found at the Mountain Seaview Apartment by a maid, leaning back on his sofa with a plastic bag covering his head and a tube running from the bag to a diving gas tank.
His legs were tied together with a rope, while his arms were free.
Chalong police Lt Attawat Suwannarat said it was not clear at this stage whether it was a case of suicide or something more sinister, but suggested that asphyxiation was the most probable cause of death.
Mr Weitz’s body was taken to Vachira Hospital for autopsy.
He was reportedly last seen alive on Monday with his female friend who shared the apartment with him, and who is believed to be his girlfriend.
Police are still trying to find the female for questioning.