Two men with a machete approached a man and woman while they were walking in Endcliffe Park in the attempt to steal their camera but were fought off leaving one victim injured.
After the mid-day report on Sunday, police did an extensive search of the scene on Ecclesall Road but were unable to find the suspects.
An investigation has now been launched and officers are looking for anyone with any information if they were around the area.
South Yorkshire Police have now set up additional patrols in the area for reassurance in the local community.
The victim was left with a hand injury that is not thought to be serious.
Detective Sergeant Matthew Penn said: “I am keen to hear from anybody who was in the park around the time of the incident”.
One of the suspects was described as being 5ft 8ins with a slim build wearing a dark hoodie and full face covering. The other was said to have olive skin.
The two suspects were said to have a local accent and to be in their late teens to early 20s.
South Yorkshire Police are asking for anyone with information to call 101 quoting the incident number 529 of 27 February.