They were arrested from Polo area of the city last evening while they were roaming suspiciously and carrying six mobile phones and 20 SIM cards.
The phones and SIM cards were seized from besides a car and a motor bike, the sources said.
Police suspected that the four were working under Jack Marak, a self-styled area commander of West Khasi Hills district.
The four were identified as Vincent T Sangma (20), a resident of Weikut village in South West Khasi Hills, Viraj Chungkan R Sangma (21) and Najim R Sangma (22), both residents of Chima Apal village in North Garo Hills district, and London A Sangma (25) of Bagli village near Borsora in South West Khasi Hills district.