Police are appealing for information about the incident, which happened in Garrad's Road last Wednesday.
Police are looking for a gang of four youths who robbed a 15-year-old boy at knifepoint for his mobile phone.
The teenager was approached as he walked along Garrad’s Road, Streatham, last Wednesday (March 7) just after 4pm.
One youth pulled out a knife and forced the boy to hand over his phone, before the others began punching and headbutting him.
They were seen running towards Streatham Common following the incident.
The suspects are described as young black men, dark and light skinned, aged between 16 and 17.
Anyone with information should call Detective Constable Leanne Snelling in Lambeth CID on 020 8649 2439, email Leanne.Snelling@met.police.uk or speak to Crimestoppers anonymously on 0800 555 111.
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