No shots were fired but the two female members of staff, aged 27 and 24, were said to be left upset by the incident.
The suspect made off with hundreds of pounds after stealing the 27-year-old's purse, police said.
The incident happ-ened at about 6.30pm on Tuesday at J'Adore Beauty, in Hillfoot Street, Dennistoun, Glasgow.
The suspect threat-ened the women with what police said "appeared to be a firearm" before stealing the purse.
He then made his escape and police are appealing for help from members of the public who may have seen the man, who was wearing distinctive clothing, including a high-visibility vest.
Detective Inspector Alan Burton, of London Road Police Office, who is leading the invest-igation, said: "The suspect made his escape on foot across Duke Street and into Bellfield Street which would have been busy with traffic and pedestrians at that time of night.
"His red jacket and high-visibility vest were very distinctive, so I'd ask anyone who saw him to get in touch.
"In the meantime we're checking CCTV footage for clues as well as carrying out door-to-door inquiries."
The suspect is in his mid 20s and around 5ft 9in tall.
He was described as gaunt and was wearing a red jacket with a high-visibility vest over the top.
Anyone with inform-ation should call London Road Police Office on 0141 532 4600 or Crime-stoppers – in confidence – on 0800 555 111.