The incident happened around 1pm on Saturday, near to Willow House Nursing Home on Toll Road in the Cellardyke area.
A 63-year-old woman was robbed of a carrier bag by a male on a bicycle, who left the area whilst a member of the public assisted the victim.
The suspect is described as being a boy of around 16 years old, wearing a dark beanie hat. He was riding a dark coloured bike.
Detective Sergeant Kevin Petrie, from Levenmouth Police Station, said: “We’re hoping to hear from anyone with any information on the crime and also anyone who can identify either the suspect on the bike or the woman who stopped to assist the victim.
“Any information could prove useful to our investigation. Please call police on 101, quoting incident 3061 of 11 July. Alternatively, you can contact Crimestoppers on 0800 555 111, if you wish to remain anonymous.”