Detectives said the hooded robber strikes at nightfall, targeting couples sat on a park bench in Brookmill Park before pulling a knife and robbing their mobile phones.
The incidents occurred between 7.45pm and 10.00pm on August 30 and 31 and September 2.
In the incident on August 31, a man in his 20s suffered a number of stab wounds. He was rushed to hospital where his injuries were assessed as non life-threatening; he continues to recover.
The robber was described by police as black, 6ft tall and skinny, wearing a face mask and hood.
Detective Sergeant Dan Rouse, of the south east command unit, said the force was working around the clock to identify the armed robber.
“We are extremely concerned by the actions of the suspect, who clearly is a violent offender,” he added.
“I urge anyone who has seen or sees a man in Brookmill Park matching the description of the suspect provided to call 999 immediately.
“Please work with us to help catch this man and remove him from the streets.”
Any witnesses or those with information are urged to call 101 ref CAD 7037/31 Aug.
