Just after 8pm on Sunday, April 16, the teenagers went into the One Stop store in Studfall Avenue.
One stood at the door while the other threatened a staff member and pulled out a carving knife.
When the staff member shouted for help, both men ran away across the green area in front of the shop.
The first offender is described as white, slim and wearing a face covering and grey tracksuit top and bottoms and the second is described as about 5ft 6in, with a medium build, white, in his early teens and wearing a grey hooded top.
Witnesses can contact police on 101 or Crimestoppers anonymously on 0800 555111.