Mini Market staff refused to hand over cash to teenagers who threatened them with what is believed to be an imitation firearm.
The two men ran from the scene empty-handed after a raid on the Bletchley store - but the victims were unharmed.
The first offender was black of slim build, aged 16 or 17 years old and was wearing dark clothing and trainers.
The second man was also black of slim build with a slim face, around 16 years old and wearing a hooded top and trainers.
DC Hayley Holloway, from Milton Keynes police station, who is investigating the attack, which happened on Tuesday at 10.45pm, said: “I am appealing for anyone who saw what happened or anyone with any information about this incident to contact police.
“If you saw anyone acting suspiciously in the area or anyone matching the description of the offenders at the time of the incident please call our 24-hour non-emergency number 101 to speak to an officer.”
If you don’t want to speak directly to the police you can contact the independent charity Crimestoppers anonymously on 0800 555 111 or online at crimestoppers-uk.org.
No personal details are taken information is not traced or recorded and you will not go to court.