The robber came off his moped as he attempted to grab a phone from a pedestrian then fled and jumped into a taxi which was driving southwest along Camden Road.
He struck at about 7.30pm on September 14 at the junction of Camden Road and Camden Park road.
After hailing the taxi and getting in the driver dropped the man off at the junction of Agar Grove.
A police statement said: “Officers are appealing for the driver of this black cab to get in contact as they may hold crucial information that could identify the suspect. No arrests have been mad and enquiries continue.”
Anyone with information is asked to call police on 101 or tweet @MetCC. To remain anonymous call Crimestoppers on 0800 555 111.