PLEASANTON (KPIX 5) — A massive search and rescue mission continued in the East Bay Tuesday as over 200 volunteers helped authorities look for a man who never returned home from a weekend run at Pleasanton Ridge Regional Park.

There are 13 local agencies now involved in the search for 37-year-old Berkeley resident Phillip Kreycik. Authorities on Tuesday afternoon estimated the search has encompassed about 16 square miles and called the effort unprecedented in scope. Some of the agencies involved are using K-9’s, fixed-wing aircraft, and drones as they comb through 50 square miles of brush and tough terrain in the Pleasanton hills.

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His wife told authorities he was planning to be gone for only an hour Saturday morning. Alameda County Search and Rescue Chief Ron Seitz said people who go missing in the county are usually found fairly quickly, and the park is popular with visitors who likely would have noticed someone needing help.

“It’s very hard to get lost here,” said Seitz.

Investigators told KPIX 5 concern over Kreycik is growing. They called Tuesday’s search critical as the area covered widens with a more organized and systematic approach.

“We specifically are going to focus on going about 100 meters off of each linear trail down deeper into the tree lines,” said Sgt. Ray Kelly with the Alameda Sheriff’s Special Operations Group.

At a Tuesday afternoon press conference, Kelly said after four days there are two probabilities: either Kreycik is incapacitated somewhere and searchers can’t find him because of that, or he is somewhere else completely.

“We’ve done an exhaustive search over the last four days,” said Kelly, adding that volunteers have found items such as watches, sunglasses, and even blood on a rock that was determined not to be human blood, illustrating the thoroughness of the ongoing search.

Avid hiker Marsha Hurd and her volunteer group were walking the hills to aid in the effort.

“Hopefully, we’ll find a father so he can go home to his children,” said Hurd.

Authorities said their search for the father of two has intensified with more detailed ground and aerial searches.

Monday night efforts continued in the air over the ridgelines using drones and the Alameda County Sheriff’s search plane, both using infrared technology. The fact that there has been no sign of Kreycik is concerning for searchers.

“With that we hold on to hope that maybe we were missing it; That Phillip is still up there and in survival mode,” said Sgt. Kelly.

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Tuesday’s search will once again stretch into nighttime if crews turn up no sign of Kreycik.

“We are continuing our investigation at this time. We don’t have any reason to believe that this is anything other than a missing person, but we’re going to continue to investigate and hopefully we find Phillip today. That’s the goal,” said Pleasanton Police Lt. Erik Silacci.

As of a Tuesday afternoon update, authorities said 16 square miles have been searched so far.

“We have two possible scenarios at this point. One is Phillip is up there somewhere in those mountains. Or number two, he parked his vehicle and is somewhere else, his whereabouts unknown,” said Silacci.

Investigators said they have found a watch and a spot of blood, neither of which belonged to Kreycik. While he was known to track his runs with the Strava app, the smartwatch he was wearing was not GPS enabled.

Alameda County investigators are hoping he found water amid the recent heat in the area.

“There’s spots out on the trail where you can get water. There’s also big troughs where there is livestock up there,” said Sgt. Kelly.

A group of well-organized volunteers are doing their own grid search.

“We’re assigning numbers, we’re checking them. We’re assigning areas according to their specific abilities. E-bikes are going further. We are doing this in a very formatted way’ a very smart way,” said search organizer Sandy Schneider.

John Cho has never met Phillip, but was connected with him on the running app Strava.

“We had two bikers and five hikers. We basically alternated every 20 feet — climbing down, climbing back up — as long as it was safe for climbing back up. It took about four hours on a two mile trail,” Cho told KPIX.

He found a water bottle and logged it into a database when his search group came back.

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“This particular water bottle was way deep in the ravine. It’s an area you can’t just hike down or run down. It kind of stood out with the lights,” said Cho.