A taxi driver felt a gun pushed to his neck before he was robbed by his passengers in the early hours of yesterday.
At around 2.15am the victim, who was in his thirties, picked up a man and a woman from Greenleys who asked to be taken to London Road, Loughton.
The woman got out of the car, but the man stayed and the victim felt what he believed to be a gun held to his neck.
He demanded money, which the taxi driver handed over, before the couple fled on foot down an alley way.
They headed through Wallmead Gardens and are thought to have continued to Whitworth Lane, where they may have got into a vehicle.
The woman is white, with long dark brown hair tied in a ponytail and wearing a dark blue/black jacket with blue jeans.
The man is white and was wearing a black coat with a hooded top.
The pair met a third man immediately after the robbery, who was wearing red trousers.
Det Con Greg Hughes said: “This was distressing for the victim and we are doing all we can to find the perpetrators.
“We would ask anyone in the area at the time who may have seen anything suspicious to please contact us as a matter of urgency.”