FILLMORE, Calif. -

Crews are desperately searching for a missing firefighter in a rugged, local forest.

Arcadia firefighter Mike Herdman went missing on Friday night.  Tuesday marked the fourth day he had been missing and the second full day of a search to find him.  Tuesday's search consisted of more than 50 search and rescue volunteers.  The crews searched the area by ground, helicopter and horseback.  They are searching a large area in the Sespe wilderness, north of Fillmore.

"It includes the ground crews that we have sent in by air and inserted them into a point where he was last seen.  We also sent our mounted unit on horseback to the point where they began their trek going in from that way in case he goes back the way he began," said Ventura County Sheriff's spokesperson Sgt. Eric Buschow.

Herdman and his friend were on day two of a four-day hiking trip, when Herdman's dog took off from their campsite and into the forest.  Herdman ran after his dog wearing only shorts, and a T-shirt.  He was barefoot and had no supplies with him.  Buschow says that happened on Friday night and that was the last time Herdman was seen.

When Herdman did not return to the campsite, Herdman's friend hiked for two days out of the remote area to call for help.

"He reported it to us that his friend was missing and we begin a search early Monday morning.  We were out here until nightfall and then we resumed the search today," said Buschow.

The search area spans for miles along the Sespe wilderness.  The spot is a popular hiking and backpacking spot but the terrain is rough and steep.  

Some of Herdman's fellow firefighters and friends have also joined in the search to find him.

Investigators say Herdman is an experienced outdoorsman and a strong athlete but are worried that the rugged terrain and cold overnight temperatures are big concerns.

Buschow said as of Tuesday night they had found some footprints near a creek but no sign of Herdman or his dog.  At this point, officials do not know if Herdman is injured or just lost.

For safety reasons, Tuesday's search was called off at dusk but the Santa Barbara County Sheriff's Department says search and rescue volunteers will be back out searching for Herdman at daybreak.