The child was on the way back from school in North Finchley at a bus stop in Sussex Ring, near Dollis Valley Greenwalk, when the attacker tried to talk to her.
As passengers boarded various buses she was left alone with him at the stop – heading westbound towards Whetstone – when he then asked her to go the park.
When she refused he grabbed her wrists and started pulling her away from the stop into the park while telling her he had a knife.
He led the victim down towards the canal and behind a tree before taking her phone, grabbing her wrist and kissing her. He then left the area.
Following the assault at 4pm on September 30, Met Police officers have this morning (December 13) released an image of a man they want to speak to.
Detective Constable Chris Finnegan from the North West Command Unit based at Wembley said: “This was a frightening attack on a young girl who has been tremendously brave in coming forward.
“I stress that sexual assaults of this nature continue to be very rare, but in the cases when it does happen we remain dedicated to supporting victims and identifying and prosecuting those responsible.”