Several people reported that a youth was acting suspiciously near their lockers in the change room in Taber on Sunday.
They told police they noticed their items were missing and when they confronted the teen, they said he showed the grip of a pistol in his pants and fled.
Police said they received a call from a woman who said a young person with a gun forced her and a male companion to sit with him on a park bench.
The teen let the woman leave and police later found some of the stolen property in his possession.
He faces three counts of robbery, one count of extortion and one count of possession of a dangerous weapon.