The robbery took place near McDonald's, off Greengate Street in Stafford, at around 4.15pm on Thursday.
Three men armed with a knife threatened the victim in the alleyway and demanded that he hand over a designer bag.
The robbers were all wearing black face masks and gloves.
A spokesman for Staffordshire Police said: "Officers are appealing for information following a robbery which took place near McDonald's, Greengate Street at approximately 4:13pm on Thursday, September 30.
"Three males approached the victim in an alleyway at the side of McDonald's and demanded that the victim – a male – handed over a small black Gucci bag. The group of offenders also produced a knife from a black rucksack and threatened the victim.
"The offenders are described as black, wearing all black clothing with black face masks and gloves. It is believed they remained at the location after committing the offence."
Anyone with information, or any CCTV footage in the area, should call Staffordshire Police on 101, quoting incident number 558 of September 30.
Alternatively, call Crimestoppers anonymously on 0800 555111.