The 41-year-old was attacked in Sunderland's Mowbray Park on Wednesday between 01:00 BST and 02:00 BST.
Northumbria Police said officers were trying to trace a man who was with the victim beforehand.
He is described as 5ft 8ins tall, of medium build with short, dark receding hair. He was wearing a Miami skyline printed T-shirt, dark jeans and trainers.
He had a tattoo on his left forearm and upper arm.
A woman has been raped in a Wearside park, police say.