Police have said “all means available” will be used to find muggers who held a knife to a boy’s neck.
Two men, believed to be aged 18 to 20, approached three 16-year-olds as they walked near the railway bridge in Alderton Hall Lane, Loughton, at 10.45pm on Friday.
The boys were also threatened with a baseball bat as they were forced to hand over their belongings, including an Armani bag, a wallet and an iPhone.
Inspector Andy Fusher said: “The criminal investigation department are investigating the crime and will use all means available to identify those involved and bring them to justice.
"Loughton CID are appealing for witnesses to come forward to identify those responsible."
There has been criticism in the community of police calls to for people to avoid shortcuts in the area, with some claiming it is unrealistic.
But Insp Fusher reiterated a call for people to avoid remote areas.
He said: “We still ask that all residents be vigilant, pay attention to their surroundings and avoid areas or situations that could make them vulnerable.
Anyone with information relating to the robbery can contact local Police at Loughton on 101.