Police are investigating the assault and are appealing for the two adults to contact them because they are potential witnesses.
The 14-year old was walking to a park at 6.30pm on Saturday, September 21, when she was attacked by three girls on a footpath that runs behind Ashby Fields primary school, off Wimborne Place.
The footpath is close to Cabot Close and the underpass beneath Northern Way.
The girl was on her way to meet a friend when the incident happened.
Eight appliances at scene of Cransley fire
Kettering town centre restaurant ready to reopen with new menu and 'surprises'
Remembering the drought of 1976 across Northamptonshire in pictures from the archive
Wellingborough military veteran John Ruddock had cache of hundreds of indecent pictures and videos
All the pictures from Florence Bark's football fundraiser in Oundle
The two adults who intervened are described as a white man in his late 50s. He is thought to be around 5ft 9in tall, of slim build and short grey hair. He was wearing a light blue stripey top.
The other passer-by was a white woman thought to be in her early 40s, around 5ft 7in with short blonde hair in a ponytail.
She was wearing a black top and was walking a medium sized dog who has a fluffy grey coat with brown patches.
Any witnesses or anyone with information should call Northamptonshire Police on 101 or they can call Crimestoppers anonymously on 0800 555111.