LOWELL (CBS) – Police in Lowell are warning residents following a string of robberies at gunpoint that began with Facebook users posting items for sale online.

Lowell police said they are investigating multiple armed robberies that took place in recent weeks in locations around the city.

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During each incident, police said the victim advertised an item for sale through Facebook.

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When the person selling the item met up with the purported buyer, the seller was robbed at gunpoint, according to police.

“Please exercise extreme caution if you decide to conduct such business,” Lowell police said in a Facebook post.

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