A man robbed two teenagers of their mobile phones in Hainault after claiming he had a knife.
It happened in Fencepiece Road at 3.40pm on Monday.
The victims, boy and girl both aged 15, were chatting at the rear of Simmons Newsagents when the man approached them and demanded they hand over their phones.
The man told them he had a knife but they did not see any weapon.
He then ran off with their devices, a white iPhone 5 and a black Samsung Galaxy, down Fencepiece Road in the direction of Barkingside.
A Met spokesman said: "The suspect is described as a white male approx 20-25 years old, 5’10” tall, wearing a black t-shirt and grey jogging bottoms.
"He had short black hair and facial stubble and spoke with an Irish accent.
"Anyone with information or witnesses are asked to contact DC Jo Hyde at Ilford Robbery Squad on 020 8345 2680 or to remain anonymous, call Crimestoppers on 0800 555 111."
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