Police Wednesday morning actively were searching for the serial knife-wielding robber, an NYPD spokesman said, with a Nassau County police helicopter hovering over portions of Floral Park and neighboring Queens.

Plainclothes and uniformed officers from Nassau County police, NYPD and Floral Park police were seen near the Floral Park Long Island Rail Road station, south of Jericho Turnpike.

The masked, knife-wielding suspect is wanted in 24 robberies since March 1, and one attempted robbery Tuesday night of a College Point discount store, NYPD said

Overall, he’s struck seven Queens small businesses and 17 others in Nassau and Suffolk counties.

A Nassau County police spokeswoman could not immediately confirm that the search was specifically for the knife-wielding serial robber.

The search comes less than 24 hours after the suspect’s attempt at a Dollar Tree store on 14th Avenue.

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Wearing sunglasses and a black handkerchief as a mask, the suspect demanded money but ran off without getting anything, police said.

It’s unclear why the suspect ran off — or if he was frightened away — without notching a 25th successful robbery since March 1, the spokesman said.

Police said after Tuesday’s failed robbery that the suspect may have jumped into a gray Nissan.

Since May 11, the serial robber has hit seven small businesses in Queens; he’s also robbed 13 Nassau spots and four in Suffolk, mostly Subway sandwich shops, Dunkin’ Donuts, Carvel ice-cream stores and 7-Elevens, police said.

The Long Island robberies date to March 1, police said.

The Dollar Tree attempt is the first time the serial robber has been known to fail, according to police.

The FBI has joined forces with NYPD, Nassau police and Suffolk police in an effort to nab the robber, who has been more daring recently.

He struck a Subway in Far Rockaway on Monday, entering the fast-food restaurant at Beach 20th Street about 9:30 p.m. and taking $600 from the cash register, police said.

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The suspect in the pattern has been described as 25 years old, about 6 feet tall with a medium build, most often wearing a dark hooded jacket, bluejeans and tan work boots. He usually covers his face with dark sunglasses and a dark cloth, police said.

Witnesses have described him carrying a large butcher knife, which police have said is uncommon in this type of crime.

With Ted Scala