Police have released the photo of a suspect wanted for robbing straphangers on the subway in Queens, Manhattan and Brooklyn dating back to August.

The suspect — identified by police as 21-year-old Richard Brown — started his string of robberies on Aug. 15 when at about 4:23 a.m. he went up to a victim on a southbound F train approaching the 75th Street station in Queens and started to talk to him, cops said. Brown then threatened the victim by saying he had a firearm and demanded his phone. Once Brown took the cell phone, he forced the victim to get off the train at 71st Street.

RELATED: PHOTOS: Two women sought in connection to Derrick Williams robbery

Brown’s next three robberies occurred all in September and also involved stealing phones from victims.

On Sept. 17 at about 6:35 a.m., Brown approached a 22-year-old victim on a southbound A train, which was approaching the Boyd Avenue and 88th Street station. Brown once again said he had a firearm and demanded the victim’s phone, according to police.  After taking the victim’s iPhone 6, Brown forced the man off the train. During this alleged robbery, a second suspect acted as a lookout.

Three days later, Brown struck twice, again accompanied by a second suspect, police said. The first was at about 1:30 a.m. when he approached a 22-year-old victim on a northbound J train and demanded his cell phone, while saying he had a firearm. He then took the victim’s iPhone 6 and forced the man to get off at the Delancey Street and Essex Street subway station in Manhattan, authorities said.

Hours later at 5:45 a.m. Brown and the other suspect went up to a 20-year-old man and 22-year-old man while on a southbound A train approaching the Jay Street-Metro Tech station in Brooklyn, police said. After saying they had a firearm, both suspects demanded the victims’ phones and took two iPhones  and a debit/credit card. They then ordered the victim off the train, police said.

RELATED: Subway rider stabbed 4 times in the butt: NYPD

The most recent robbery occurred on Dec. 12 at about 7:25 a.m.  onboard a northbound A train. Brown went up to a 17-year-old boy, started talking to him and then took the boy’s Samsung Galaxy phone. He threatened the boy when he tried to get the phone back. Brown then ordered the victim to get off at the Grant Avenue subway station. 

Brown is described as a black man, standing about 5 feet 10 inches tall, and weighing 160 pounds. He has brown eyes, black hair, and tattoos on his face, neck and hand.

Anyone with information about the incident is encouraged to contact the NYPD's Crime Stoppers hotline at 1-800-577-TIPS. Tipsters can text information via 274637 (CRIMES) and then entering TIP577, too. 

The public can also submit tips online at www.nypdcrimestoppers.com.