A foreign couple contacted the Pattaya police after they emerged from the sea to find their possessions missing early this morning.
Iranian Sajjad Falahatpishen, 36, had entered the water for a swim with his Russian wife leaving their things on the beach.
Missing was a phone valued at 30,000 baht, 1,000 baht in cash, their room key and other items.
Nawin Sasomthong, 25, a mat rental vendor, said he saw a man in the immediate vicinity who may have been involved.
He drove off on a Honda PCX.
Police are investigating.