Police say two robberies committed within five minutes of each other in Swansea were probably linked.
A man threatened a 20-year-old student with a knife near Singleton Park around 1615 BST on Wednesday before taking his iPod and running off.
Soon after, an 82-year-old man walking down a nearby lane was also confronted by a man with a knife.
The suspects in both incidents were white males thought to be in their early 20s.
Following the first robbery the suspect ran into church grounds at the junction of De La Beche Road and Gower Road.
The suspect was about 5ft 10in (1.7m to 1.8m) tall, with short facial hair on his chin and short light brown hair.
Police said he spoke with a local accent and was wearing a green hooded top which had white lettering on the chest, blue jeans and trainers.
The second incident occurred five minutes later as the 82-year-old man was walking through a lane leading from the park alongside Sketty Surgery to De La Beche Road.
Again the suspect demanded money - but he left empty handed.
The suspect was about 5ft 8in to 5ft 10in (1.7m to 1.8m) tall and had light brown or blond hair.
Police are appealing to people who may have seen anyone in Singleton Park fitting the descriptions between 1600 and 1700 BST on Wednesday to contact them.
Insp Chris O'Brien added: "The suspect was clearly desperate for money to feed a drug habit and an investigation is ongoing to trace this person."
Contact South Wales Police on 101 or Crimestoppers anonymously on 0800 555111.