An armed robbery took place at RV News in William Street on Friday night.
Four men wearing masks threatened the shop assistant, 28, with a black hand gun.
They took cash from the till and cigarettes before leaving the scene on foot.
Det Con Tracey Joyce said: “The shop assistant was luckily uninjured but this was a shocking experience as one of the offenders threatened the victim with what appeared to be a black hand gun.
“The offenders spread themselves out throughout the shop and one guarded the door whilst the offence was taking place. It is possible that they had visited the area before to plan the incident and I would urge anyone who saw the four leaving the shop or anyone who saw someone acting suspiciously in the area prior to the incident to contact the police.”
The first offender had a medium build and wore a black padded jacket, light grey or white jogging bottoms, black gloves with a white emblem on the top and a black face mask.
The second offender had an average build and wore a blue hooded top, a black waistcoat, blue tracksuit bottoms and black training shoes.
The third offender wore a large blue padded jacket, grey bottoms, a grey hooded top and a black ski mask.
The fourth offender wore a black padded jacket with a black ski mask covering his face.
Call Det Con Joyce, at Luton Police Station, in confidence on 01582 394086, or Bedfordshire Police on 101, or text information to 07786 200011.
Alternatively you can contact the independent crime fighting charity Crimestoppers, anonymously, on 0800 555 111.