The incident happened between 11.30pm on Friday, May 24, and 12.15am on Saturday, May 25, when a man walking through the park was approached by two others.
The men stole two phones off him, a Galaxy Note9 Hybrid Slim and a Oneplus 6T, before making off.
The first suspect is described as white, in his 20s, about 6ft and slim and with stubble on his face.
He was wearing a black hoodie, blue jeans and white trainers.
The second suspect was white, slim and about 6ft.
Anyone who saw the incident or has information about it should call Northamptonshire Police on 101, or Crimestoppers anonymously on 0800 555111.