A police officer identified Pol Sgt Siriraj Runjuan suspected to be the gang leader remains at large.
The arrest of the gang came after a Russian couple alerted the police after they were kidnapped from Haad Rin beach and taken into a car to a place to demand ransom on Tuesday.
The kidnappers then abandoned them at a place in Ban Thong Sala and drive off.
Investigation later by police showed five men, including the police sergeant were responsible for the extortion.
Four were later arrested. They are Apidet Kongman, 31, Narin Sikaew, 46, Suriya Ruangthong, 47, and Thaweesin Kongnark, 34.
They were charged of extortion, illegal detention of others, body assaults, and robbery.
Hunt is still on for the gang leader who was believed to return to his hometown in Nakhon Si Thammarat for hiding.