A source told NBCLA.com the missing deputy was identified as Deputy Zoltan Tombol. On Sunday, Tombol's wife reported him missing to police.
It's unclear how long Tombol has been missing. Tombol lives with his wife in Yorba Linda.
On Monday night, Brea Police discovered Tombol's vehicle in the city of Corona near Green River Road and the 91 Freeway, south of the freeway. Several jurisdictions converge on the location, so Brea Police elected to take lead of the investigation.
Searchers were concentrating along a fire access road since Tombol is know to be an avid hiker and runner. Brea Police were told the fire road is one of Tombol's regular routes.
Police do not suspect foul play.
"This man is very conscious and aware of the terrain he is in now," said sheriff's spokesman Steve Whitmore. "So the fact that he missed that appointment has us concerned and we will continue looking for him."
They planned to launch a helicopter again Tuesday to help search the area.