The incident happened at around 3.30pm on February 8 in Beckenham Lane in Shortlands when police were called to reports of a “knife robbery”.
Having arrived, officers arrested four teenage boys aged between 14 and 17 who remain in custody for questioning.
A knife was also seized and there were no reported injuries.
A Metropolitan Police spokesperson said: “We were called to Beckenham Lane, Shortlands at around 15:30hrs on Saturday, 8 February to reports of a knife robbery.
“A teenager is reported to have been robbed by a group of teenagers.
“Officers arrived on the scene quickly, made four arrests and seized a knife.
“Those arrested – all teenage boys and aged between 14 and 17 – remain in custody for questioning.
“There were no reported injuries.”
