FILLMORE, Calif. -

There are new developments Wednesday evening in the search for an Arcadia firefighter lost in the Sespe Wilderness, north of Fillmore.

Late Wednesday afternoon searchers spotted a dog in the search area.  Sgt. Eric Buschow with the Ventura County Sheriff's Department can't confirm if the dog is Mike Herdman's dog, but Buschow says it does match the description of Herdman's dog.

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 said that happened on Friday night and that was the last time Herdman was seen.

The Ventura County Sheriff's Department has activated the state mutual aid system.

 "What that means is we bring in agencies from the surrounding counties.  So today we have Los Angeles County, Orange County,  and San Luis Obispo County and we brought out the Civil Air Patrol too," said Deputy Chris Dyer with the Ventura County Sheriff's Department.

Wednesday marked the fifth day Herman had been missing and the third full day of a search to find him.  Wednesday's search consisted of more than 50 search and rescue volunteers.  The crews searched the area by ground, and helicopter.  The newest addition to the search team on Wednesday included three search dogs.

Search and rescue volunteers plan on continuing their search for Herdman Thursday morning.