"When they did not give it over initially they thought at most they may be involved in a fight, however they had a gun pointed at them until they handed all their stuff over," she said in the post.
Armstrong confirmed three teenagers were approached by a larger group of people and had threats made against them, before having personal property stolen.
"It was reported to Police one of these offenders presented a firearm," he said.
Armed police staff responded to this incident and later located the six involved in the incident, all youths, at nearby Morningside Train Station.
"They were taken into custody and Police also recovered stolen property at the time."
Armstrong said no firearm had been located by police.
"Thankfully, the three victims were not injured in this incident, however they are understandably shaken by the incident."
Police are currently making further enquiries, however the matter will be referred to Youth Aid.