Police are looking for this man, who they say has been touching women on the 1 train since as early as 2011. View Full Caption NYPD

MIDTOWN — Twin sisters were groped by the same man aboard a 1 train in Manhattan about five years apart, police sources said.

Police were investigating a forcible touching incident in which a man touched an 18-year-old woman's thigh aboard a 1 train at the Times Square station roughly 5:40 p.m. on Sept. 21, the NYPD said.

When the victim's sister saw a photo of the suspect Friday, she recognized him as the same man who touched her aboard the same train five years ago, police said.

That incident took place at the 110th Street stop sometime between Sept. 2011 and June 2012 when the girl was 13 years old, police said.

In a separate incident, police say the man also sat next to a 24-year-old woman and rubbed the outside of her thigh at the 66th Street stop on Sept. 19 about 5:40 p.m., police said.

She was not related to the sisters, sources said.

The suspect is believed to be in his 40s and standing about 6-feet tall. He was last seen wearing a green T-shirt while carrying a black backpack.

Anyone with information is asked to call Crime Stoppers at 1-800-577-TIPS.