Karon Police were alerted to the situation at about 3:50pm.
Three tourists had entered the surf to swim, police were told.
Two of the tourists, identified as Miss Asilo Junarra Heyzel, a British national, and Mr Faisal Fadel Mohammed Hasan, a Yemeni national, were rescued by lifeguards.
However, Mr Luvovadio Allan Deraut J., a Belgian citizen, remains missing.
Karon Municipality has set up a special center to coordinate the search for the missing tourist as the search effort continues.