A group of teenagers wearing Scream-type Halloween masks attacked a 22-year-old woman in Greater Manchester.
She was dragged to the ground after being followed along Sunningdale Road in Denton and sexually assaulted by four teenagers. She fought the gang off and called for help.
Police said one youth was chubby and in his early teens, while another was tall and wore white trainers.
Superintendent Neil Evans of Greater Manchester Police said the victim had suffered a "traumatic ordeal".
"Given the offenders were wearing masks designed to be scary means it must have been a truly harrowing and scary few minutes for this woman," he told Manchester Evening News.
"She was pushed to the floor and sexually assaulted, leaving her in a state of total shock and clearly she is extremely distressed.
"Anyone who has been a victim of sexual assault will know just how frightening it must have been for this victim, and given the offenders were wearing masks designed to be scary means it must have been a truly harrowing and scary few minutes for this woman.
"The purpose of this appeal is not to unduly alarm the community but it is important we let people know what has happened so they can both be vigilant and help us track down these cowardly offenders.
"If you know of anyone who might be involved, then please call us. If you are a parent and you know your child went out with friends dressed in these type of masks and you have suspicions then please, do the right thing and call us.
"This woman has suffered a terrible ordeal and we need, for her sake and the wider community, to catch the culprits. We are conducting a number of inquiries in the local community and I want to assure people we will do everything we can to find those responsible."