Police are asking for help finding a man they say sexually assaulted a woman in Brooklyn Wednesday.

Investigators say the man - seen in surveillance video - attacked the 33-year-old victim in the stairwell of her apartment building in East Flatbush.

He also stole her cell phone and cash from her purse.

The attacker is described as being 18 to 25 years old, 5'8" tall, weighs 155 pounds and has a medium complexion.

Police say he was wearing a black and white winter hat, a black jacket and camouflage pants.

He also had a bicycle.

Anyone with information on the case should contact the Crime Stoppers hotline at 1-800-577-TIPS, or text CRIMES and then enter TIP577, or visit www.nypdcrimestoppers.com.