A 16-year-old who became separated from her friends at a fireworks display in Birmingham was seriously sexually assaulted by a group of teenage boys.
The girl was at the event in Pype Hayes Park on Friday when she was approached by four boys who offered to help her find her friends, police said.
She was led to a lake in a separate part of the Erdington park and then to a toilet area where she was attacked.
Police have released an e-fit of the main offender.
Det Insp Jon Thursfield, of West Midlands Police, said: "This was an extremely traumatic attack on a young girl who had just come out for a night out with her friends to enjoy the fireworks.
"We are working extremely hard to identify who has done this so that we can bring them to justice."
He said the public had a vital role to play in identifying the boys.
They were aged between about 15 and 17 and waited in a queue for the toilets.
The first boy was described as white, about 5ft 6ins (1.67m) tall, of stocky or chubby build, with very blue eyes, tidy eyebrows and a pointy nose.
He was wearing a purple, Adidas, hooded tracksuit top and grey Adidas tracksuit bottoms with purple stripes down the side.
The second offender was described as mixed race, about 5ft 6ins (1.67m) tall of slight build, with short black hair. He was wearing all black clothing and a black scarf pulled up over the bottom half of his face.
The third offender was described as white, chubby build, and had short dark hair, with freckles on his face and bushy eyebrows, one of which had a shaved line in it.
The fourth boy was described by police as white, medium build, aged about 15 or 16 years old, with short, dirty-blonde hair and blue eyes.