Nassau County police are stepping up patrols around retail stores with plainclothes and other special unit officers in an effort to catch a lone masked gunman who since August has made off with at least $13,000 in 14 holdups across Long Island.

“We’re extremely concerned about this robbery pattern,” Det. Lt. Richard Lebrun, commanding officer of Nassau’s Public Information Office, said Monday. “We have dedicated a large amount of resources to patrolling in areas that he might hit again. . . . Hopefully we get some tips and no one gets hurt.”

The suspect often has used zip ties or handcuffs to bind customers and workers, and forced employees to open safes or cash registers, police said.

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The latest robbery happened Monday morning when the masked gunman forced his way inside a Westbury Babies R Us, police said.

The holdup added to a tally that includes eight stores in Nassau and six in Suffolk since Aug. 20, police said. In each robbery, witnesses described the suspect as a man wearing a black mask and dark clothes and carrying a black handgun.

No one has been hurt in the robberies, but police urge the public and retail employees to be on alert — and to comply with any robbers’ demands.

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The thief has gotten away with between $800 and $5,200 during each robbery in Nassau, police said.

Suffolk police declined to say how much the robber has netted.

Anyone with information can call Nassau County Crime Stoppers anonymously at 800-244-8477.

With Patricia Kitchen