Teams from several agencies searched Koh Lipe and the surrounding sea on Thursday for an American tourist who went missing early on Tuesday.
Satun police, tourist police, immigration police, troops and harbour officials continued the search after two friends reported that Charles Alexander Kosydar, 39, disappeared early on Tuesday.
They told police they were drinking with Kosydar on Monday night until the early hours of Tuesday and the American left to swim at Pattaya Bay and did not return.
Officials also checked an area about six nautical miles from Koh Lipe after fishermen reported they saw something that looked like a human body but they found nothing.
Kosydar entered Thailand via the Suvarnabhumi Airport immigration checkpoint on October 18 with three friends.