Officials identified the suspects from CCTV footage after two Japanese men, a Thai woman and a Canadian man separately complained to tourist police that they had lost their wallets and cash last week, The Nation Thailand reported.
The stolen money reportedly amounted to over 260,000 baht ($7,575).
The footage shows the three Mongolian suspects and two female accomplices, who are still at large, approached the victims near a currency exchange booth after they had just exchanged money.
Police are hunting for the other two members of the gang.
Thailand is stepping up campaigns to crack down on foreign criminals as Southeast Asia’s second largest economy prepares to receive 30 million foreign tourists this year.