A robber threatened a 15-year-old boy at a Tube station as he stole £3 from him, police said.
Detectives have released CCTV images of a man they want to speak to in connection with the incident at Wembley Park station.
The teenage victim was allegedly approached as he waited on the northbound Jubilee Line platform at around 8.20am on Sunday, November 16.
Police said the man asked the boy for £1, which the boy gave him.
He is then said to have become aggressive and demanded all the money the teenager had in his wallet.
After the man allegedly threatened the boy with violence, he took the remaining £2 from his wallet and demanded the phone.
The boy then ran away and boarded a train, police said.
Detective Constable Carl Wayte said: "While the amount stolen in this incident was relatively small, the victim felt intimidated and was left in no doubt the man was prepared to use violence."
Anyone with information is asked to contact British Transport Police on 0800 40 50 40 or text 61016 quoting reference TSUB/B5 of 12/12/2014. Alternatively, contact Crimestoppers anonymously on 0800 555 111.
