At around 4.30pm on Monday, 22 March the girl got on a bus towards Lewisham.
When she got off the bus, she walked towards Pepys Park where she sat on a bench near the football cages.
A boy approached her. He was joined by two other boys who are alleged to have stolen her phone and ran off.
The victim and boy are then reported to have followed the pair to another part of the park, where the three boys are alleged to have pinned her down and raped her.
Police have released descriptions of the teenagers who are understood to have carried out the attack:
The first is described as black, aged approximately 16/17, with no facial hair. He was wearing a blue beanie, a black ‘Kings Will Dream’ coat with fur around the hood and black and grey trainers. He also has silver caps on two of his teeth.
The second is described as a lighter-skinned black boy, age approximately 16/17, with two earrings, one stud in each ear lobe. He had a high-top hairstyle with slight stubble. He was wearing a black Zavetti, knee-length coat with a yellow and red brand mark on the sleeve.
The Third is described as a lighter-skinned black boy, age approximately 16/17, wearing a durag. He had a black coat and black tracksuit bottoms on.
There have been no arrests and enquires are ongoing.
Detective Constable Daniel Weeks, who is leading the investigation, said: “We are doing our utmost to provide the victim with support from specially trained officers following this horrific incident.
“I am asking members of the public who were in the park that day to think carefully about whether you saw the males described. Did you see anyone acting suspiciously? What were they doing and where did they go? No matter how small or insignificant you think your information might be, it could be hugely significant for our investigation.”
Any witnesses or anyone with any information is asked to get in contact with police via 101 or tweet @MetCC and quote CAD: 7933/01APR21 Alternatively, call the independent charity Crimestoppers anonymously on 0800 555 111.