A 20-year-old man was stabbed in the incident after the mugger ambushed him and his friends in Judge Heath Lane, Hillingdon.
The thug approached the group and demanded they empty their pockets at 1.35am on 8 April.
He then charged at the group, tripped up the victim and stabbed him in the chest.
The victim was taken to hospital for treatment and his injuries were assessed as not life-threatening.
No property was taken during the incident.
Detective Constable Ella Turvill, leading the investigation, said: “This incident has had a significant impact on the victim both physically and mentally.
“We are working to urgently identify the man who carried out this attack and I hope that the e-fit image may jog someone’s memory.
“Anyone who recognises the man in the e-fit should contact us as soon as possible.”
Anyone who recognises the man in the image or have any information that could help the investigation are asked to call police on 101 or post @MetCC and give reference CAD 518/08Apr. To remain anonymous contact Crimestoppers on 0800 555 111.
