Robbers most recently struck the Stop In Market, 3211 S. Roan St., shortly before 11 p.m. Sunday.
Employees at the store told police two white men dressed in hooded sweatshirts came into the business with bandannas covering their faces and demanded money.
The men, one of whom was armed with a handgun, fled on foot from the store with an undisclosed amount of money.
Store employees described the robbers each as about 6 feet tall and weighing somewhere around 150 pounds. The suspects are believed to be in their 20s, police said.
Just after midnight Thursday, two men with similar builds entered Roadrunner Market, 1310 Cherokee Road, and made off with cash and cigarettes after brandishing a semiautomatic handgun.
The robbers in Thursday's incident wore hooded jackets and covered their faces with bandannas, police said.
"I can't say right now whether they are the same people in both of these robberies, but the descriptions are similar in both incidents," said Lt. Matt Howell of the Johnson City Police Department. "I don't think there's any pattern to indicate whether or not someone will hit more than once. But it seems in the ones we have had recently, the same people have hit multiple businesses."
Sunday night's robbery marks the 12th of its kind in Johnson City this year alone. Authorities have made arrests in all but four of the incidents. Of those remaining four, one case is inactive, while the three most current robberies are actively being investigated.
Last year, Johnson City police worked a total of 14 robberies at convenience stores, gas stations and a liquor store.
To help police in solving and preventing robberies of this kind, Howell recommends store owners remove anything in windows that would prohibit an officer from seeing inside the business and check security cameras to be sure they are at the correct angle to capture people as they enter and exit the store.
Store employees who encounter a robber should comply with his or her demands and try to remember any unique features that would make it easier to identify the suspect later, authorities said.
Anyone with information regarding the city's recent robberies is asked to call the JCPD at 434-6166, or to remain anonymous, call 434-6158.