A teenager girl has been sexually assaulted in a car after being picked up on a fashionable cafe strip in Sydney's inner west.

The 14-year-old girl was approached by four men in a black four-wheel drive as she walked along Norton Street, in Leichhardt, about 5pm (AEST) on Tuesday, police said.

"It's reported the girl was taken to a laneway parallel to Lilyfield Road where she was sexually assaulted in the vehicle by one of the men while allegedly being held down by the other two men," a NSW police statement said.

The girl ran home after being released from the vehicle.

She was taken to Royal Prince Alfred Hospital for examination.

Joint Investigation Response Squad Commander Paul Devaney urged parents to sit down with their children and reinforce the "Safe People, Safe Places" messages.

"Children should avoid walking on their own especially in the late afternoon or evening," Commander Devaney said.

He said young people should be encouraged to walk with other family members, friends or an adult they know, and stick to main roads and paths that are well-lit.

Anyone who has information about a black 4WD with four males acting suspiciously in the area should contact Crime Stoppers on 1800 333 000.