A woman was sexually assaulted while waking her dog in Hemel last month.
The attack took place in the Barnfield area at around 6.15pm on Wednesday, December 3.
The victim was bending down to tend to her dog when she was approached from behind and touched inappropriately.
They then ran away along Barnfield.
The suspect is described as having thick wavy blond hair, of medium build and between 5ft 7 ins and 5ft 8ins.
They wore a black puffa-style jacket, a lighter coloured hood which was either part of the jacket or from a hoody worn underneath, dark jeans, and light coloured trainers.
The victim was unable to see if the suspect was male or female but believes them to have been in their mid-teens.
Investigator Deborah Newsham said: “The woman is being supported by officers as we investigate the circumstances around the incident and try to trace the person responsible.
“I am appealing for anyone who may have information about the incident to please come forward.”
Anyone with information about the incident is asked to contact Herts Police on 101, quoting crime reference D1/18/88.
You can also report information online at www.herts.police.uk/Report
Alternatively, you can contact Crimestoppers, anonymously, on 0800 555 111 or online at www.crimestoppers-uk.org No personal details are taken, information cannot be traced or recorded and you will never need to go to court.