The incident occurred at around 5.10 pm on Wednesday, July 31, when it was reported that the victim was approached and assaulted in Six Hills Way.
The suspect was described as a black teenage girl aged approximately 13 to 14.
PC Emily Brason, who is investigating, said: “This was understandably a distressing incident, and I am appealing for anyone with information to please come forward.
“Were you in the area at the time and saw what happened, or have any further information to assist our investigation? Please email me at Emily.Brason@herts.police.uk.”
You can report information online at herts.police.uk/report, via online web chat at herts.police.uk/contact, or by calling the non-emergency number 101, quoting crime reference 41/63016/24.
Alternatively, contact Crimestoppers anonymously on 0800 555 111 or online at crimestoppers-uk.org.
If you or anyone you know have been affected by the people highlighted in this article, then please report those individuals to the Police on 101 (999 if an emergency) or visit their online resources for further details of the options for reporting a crime. You can also make a report at Crimestoppers should you wish to be completely anonymous. There is help available on our support links page.