CHICAGO (CBS) – Chicago police issued an alert of several armed robberies that happened over the President's Day weekend on the city's North Side.

Six of the robberies happened between 6:30 p.m. and 11:50 p.m. Sunday. The last happened Monday afternoon around 1:30 p.m.

In each incident, three or four armed men approached victims on the sidewalk and demanded their property by threatening the use of force. They would take the property, return to a waiting car, and leave the scene.

Incident locations and times:

• 1500 block of West Ardmore Avenue on Feb. 18 at 6:30 p.m. in Edgewater.
• 5500 block of North Rockwell Street on Feb. 18  at 7:30 p.m. in Lincoln Square.
• 5100 block of North Wolcott Avenue on Feb. 18 at 7:55 p.m. in Ravenswood.
• 2600 block of West Gregory on Feb. 18 at 8:55 p.m. in Lincoln Square.
• 3000 block of West Peterson Avenue on Feb. 18 at 11:40 p.m. in West Ridge.
• 5600 block of North Talman Avenue on Feb. 18 at 11:50 p.m. in Arcadia Terrace. 
• 2600 block of West Albion Avenue on Feb.19 at 1:30 p.m. in West Ridge. 

The offenders were described as Black men between 18 to 25 years old wearing all dark-colored clothing and face coverings. One of the offenders wore a white face mask.

They were last seen in a dark or black colored four-door sedan.

Anyone with information about the robberies is asked to call police.