The incident occurred at about 2:35 p.m. at Grossmont Center.
One of the suspects, whom police described as either black or Latino, was armed with an unknown handgun. He did not threaten anyone with it, police said.
The suspects fled in a tan sedan of unknown type in an unknown direction.
Crime Stoppers is offering up to a $1,000 reward to anyone with information on the suspects.
The La Mesa Police Department can be reached at (619) 667-1400. Crime Stoppers has an anonymous tip line at (888) 580-8477 and can be emailed or texted anonymously at wwww.sdcrimestoppers.com.