About 300 police officers joined in the search for the 29-year-old suspect, accused of shooting his boss in the head shortly after arriving at work Tuesday morning, then killing a co-worker before fleeing to Woods.
Local prosecutor Eric Maurel urged the man to surrender on Wednesday.
“I ask him to listen to reason, to lay down his arms and to explain what prompted him to act within the framework of a peaceful surrender,” Maurel told reporters.
A sawmill worker, who witnessed the killings in the village of Plantiers, told investigators the gunman pulled out a gun after being reprimanded for not saying hello when he got to work.
Stunned by the attack, another colleague tried to intervene, but the suspect also shot him in the head, the witness said.
Investigators said the man had recently clashed with his boss over his working hours.
Police backed by helicopters continued to scour the cave-dotted mountains on Wednesday in search of the suspect, described as an avid hunter who had at one point spoken of becoming an army sniper.
The rugged Cévennes, a bastion of French Protestantism located north of Montpellier, are one of the most remote regions in France.
Many members of the French Resistance hid in the caves and forests of the region during World War II.