A man used a large knife to threaten another man in Slough and steal his phone and bank card, according to police.
The victim, aged in his twenties, reported being approached by two men at 11.30pm on October 31 along the canal towpath next to Goodman Park, one of which robbed him.
The victim was not injured and the two men made off on a silver bicycle.
Thames Valley Police have released an E-fit of a man they want to speak to in connection with the incident.
Police described the offenders as two black men, approximately 30-years-old, between 5ft 10ins and 6ft tall.
One was wearing a dark/grey puffer jacket. Police believe that one spoke with a Somalian accent.
Investigating officer Detective Constable Sasha Lakovic, based at Slough police station, said: “This was a frightening incident for the victim and we have been carrying out a thorough investigation.
“We are releasing an E-fit and would ask anyone who may recognise this person or has information regarding this incident to please contact us.
“You can report information through our online reporting pages, or by calling 101 quoting the reference 43220491192.
“If you do not wish to speak to the police you can contact the independent charity Crimestoppers on 0800 555 111, 100% anonymously.”