Two men were robbed while walking in Daventry Country Park.
The incident happend on Thursday July 28, at around 10.15pm.
The victims, two 21-year-old men, were walking through the park when they were approached by three other men who threatened them and stole a mobile phone.
Witnesses to the incident, or anyone with information, are asked to call Northamptonshire Police on 101. Alternatively, they can call the independent charity Crimestoppers anonymously on 0800 555 111.