The victim was out walking when he was approached by a group of around six youths – some of whom were on pedal cycles – who pushed him into a nearby alleyway.
One of the group produced a knife and held it to the victim’s throat, before demanding valuables.
The same offender then head-butted the victim before removing his mobile phone from his pocket.
At that point a member of the public disturbed the group and they made off.
The incident occurred at around 8.45pm on Tuesday (June 21) on Winckley Road.
Now police would like to speak to anyone with information about the incident, or who knows who the attackers may be.
DC Darren Caunce, from Preston CID, said: “The victim has been left incredibly shaken by this vicious incident and we are determined to find those responsible.
“Anybody who witnessed a group in the vicinity of Winckley Road, heard or saw the incident or who has information about who the offenders might be is urged to get in touch.”
The main offender is described as a white male, in his late teens, of slim build and approximately 6ft tall. He was wearing a black balaclava, dark-coloured clothes and a CP Company hat with goggles on top.
Another member of the group is described as a white male, in his early teens, with short, dark hair that was short on the sides and styled on top. He was wearing a black bubble gilet and black tracksuit bottoms.
The rest of the group were wearing balaclavas but are also believed to be white males.
Anyone with information can contact Lancashire Police on 101 quoting log number 1612 of June 21st, 2016.
Alternatively Crimestoppers can be contacted anonymously on 0800 555 111 or online at crimestoppers-uk.org.