Three suspects have robbed a dozen men at gunpoint across the borough since early last month, authorities said. The thugs kicked off their spree at about 3:45 a.m. on April 9, mugging a 29-year-old man on East 165th Street near Tiffany Street in Longwood, ­police said. They pulled a gun and fled with the victim’s cellphone, bank card and an unspecified sum of cash, cops said. The crew’s most recent strike came on April 24, when they trailed a 32-year-old man into the elevator of a Baychester apartment building at about 12:30 a.m. The crew fled with the victim’s cellphone and cash, authorities said. Investigators released surveillance images of the suspects hanging out at a Dunkin’ Donuts shortly before an April 15 holdup near Crotona Park East and Southern Boulevard.

Police are searching for the thief who grabbed packages from the back of a FedEx truck in Williamsburg, sources said. While the 30-year-old driver was making a delivery on Roebling Street near South Ninth Street at about 12:30 p.m. Monday, a sticky-fingered passer-by quickly grabbed two packages from the truck, police sources said. The driver became aware of the theft only when he arrived at the ­Atlantic Avenue delivery destination of the missing packages and couldn’t find them. Investigators did not immediately release a description of the suspect or the contents of the packages.

A pedal-pushing crook snatched a woman’s cellphone while she was snapping a selfie on a street in East Williamsburg, said law-enforcement sources. The 23-year-old victim was lining up the glam shot on Bogart Street near Harrison Place at about 11:30 p.m. Tuesday when a man sped by on a bicycle and ripped the Samsung Galaxy from her hand, sources said. A description of the suspect, who was furiously pedaling a BMX-style bike, wasn’t immediately available.

A man was caught stealing a purse in Elm Park from a woman he believed was a prostitute — but she was actually an undercover police officer, sources said. The cop was posing as a streetwalker for the NYPD’s Operation Losing Proposition near Richmond Terrace and Maple Avenue at about 12:10 a.m. on April 25 when suspect Ray Bell strolled by and allegedly grabbed the bag she had left hanging on a fence, said law-enforcement sources. Bell, 58, was quickly nabbed by the undercover cop and another officer. After they put the suspect into the back of a squad car, he went berserk and allegedly kicked out a rear window, sending a hail of glass flying, sources said. Bell, of St. George, was hit with a slew of charges including petit larceny and criminal mischief.