Victims were threatened with a handgun in three linked robberies in Kenton.
A man kicked and punched a 38-year-old victim and stole his wallet on Gooseacre Lane, at around 10.50am on April 29.
The same suspect is believed to have struck again six days later armed with a handgun and covering his face with a bandana.
He used the handgun to steal a wallet and phone from a 17-year-old victim at 5pm in Hillview Avenue on May 5.
This time he was accompanied by another male who was unarmed, police said.
At around 2pm the next day, three robbers returned to the same street and threatened a man and a women, aged in their 20s.
They punched and kicked the male victim and threatened them with the handgun.
Police say they did not manage to steal anything after the woman screamed for help.
The lone suspect in the first robbery is believed to have been the man with the gun in the second robbery and the attempted robbery.
Brent police are appealing for information and witnesses following the three robberies but have not yet released a description of the suspect.
After each robbery, the suspects headed towards Brookfield Crescent on foot.
Anyone with information should call DC Karen Beck at Brent CID on 020 8733 3709 or through Police 101. To remain anonymous call Crimestoppers on 0800 555 111.