The young victim was attacked on 29 June at around 2.50pm, since then a dedicated team of detectives has worked to trace the sex attacker.
The girl was walking through Babbs Mill Park when she was attacked.
She suffered a cut to the neck from a knife and was treated in hospital before being discharged; she continues to be supported by specially trained officers.
Hundreds of hours of CCTV footage has been viewed and nearly 1,300 homes in the area have been visited.
Three people have been arrested in connection with the investigation, but all have been released without further action.
Officers have also worked with experts to build up a psychological profile of the suspect and there have been patrols in the park every day since the attack.
The 11-year-old’s family have been kept updated.
While the image was drawn up in the days after the attack, it has only now been possible to release it to the public.
Det Insp Joe Davenport, leading the investigation, said:
“This has been a huge investigation, involving officers and specialist staff from around the force.
“I’m releasing the artist’s impression today because most of the work collecting witness statements and viewing CCTV has now been completed, and it was important to focus on gathering that time critical, local information first.
“I’d urge people to take a close look at the image. Is it someone you know? Is it someone you’ve seen out and about in the area. We need to hear from you, even if it’s so that we can rule somebody out of our investigation.
“We are determined to bring this dangerous man to justice, and the information you provide could be pivotal.”
The attacker is described as white, slightly tanned, with short brown/greying hair. He has blue eyes, large hands and a muscular, stocky build.
He was with a white King Charles spaniel, which had light brown patches on its ears and body.
Anyone with information should call our 24hr hotline on 0121 251 0277 or e-mail address email@example.com.