The robbery took place at about 1:50 p.m. Aug. 8 on New York Avenue near Church Street, detectives said.
"An unknown suspect pulled two yellow metal chain necklaces off of a male victim," the Crime Stoppers news release said. "The second male tried to assist the victim, who is his brother, and the suspect knocked the second male to the ground and took $15 from him."
The suspect fled east on Church Street.
Anyone who can help identify the suspect in the photographs is asked to call the Suffolk County Crime Stoppers confidential tip line at 800-220-TIPS. Crime Stoppers offers cash rewards for tips that lead to an arrest.