CHICAGO (CBS) — Police are warning the public about two males who are purporting to sell cellphones on social media, then rob the victims when they arrive on the South Side to complete the transaction.

The suspects make arrangements via social media to meet with citizens in public under the pretense of selling a cellphone, according to a community alert from Chicago Police. When the victims arrive to complete the cash transaction, the robbers brandish a firearm and demand their money.

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The robberies happened:
– at 4:30 p.m. Nov. 12 in the 6300 block of South Ellis;
– at 4:40 p.m. Nov. 12 in the 6300 block of South Ellis;
– at 2:30 p.m. Nov. 19 in the 6300 block of South King Drive; and
– at 4 p.m. Nov. 24 in the 6100 block of South Wabash.

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One of the suspects is described as a black boy about 17 years old, 5-foot-11 and 250 pounds with black hair and brown eyes, police said. The other is described as a black man between 19 and 22 years old and 5-foot-8 to 6-foot.

Anyone with information is asked to call Area Central detectives at (312) 747-8384.

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(Source: Sun-Times Media Wire © Chicago Sun-Times 2016. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed.)