As a fourth day of searching for a man missing in the Pleasanton hills since Saturday drew to a close, law enforcement officials announced their decision on Tuesday afternoon to scale back the effort.

The search for Philip Kreycik, 37, of Berkeley has gripped the Tri-Valley and brought out hundreds of locals, eager to offer their time and tackle 9,090 acres of tough terrain and hazards like poison oak and rattlesnakes in Pleasanton Ridge Regional Park to find the avid runner.

Coordinators said so many residents showed up to help look for Kreycik on Tuesday morning that some were turned away due to reaching "saturation for volunteers."

Despite expanding the search area 100 meters outside of his intended route and their "exhaustive search efforts," officials from the Pleasanton Police Department said in a statement that "no significant clues were collected" as of late Tuesday afternoon. Blood was found on a rock earlier during the day but testing confirmed it was animal blood.

"This was not an easy decision to make, and our focus is to continue supporting the Kreycik family," Lt. Erik Silacci said. "We thank all of the search and rescue crews as well as the hundreds of volunteers who rallied together and remain committed to locating Philip."

Kreycik was last seen at the Moller Ranch staging area at around 10:45 a.m. Saturday. His wife reported him missing when he didn't return from an hour-long run that afternoon on the Pleasanton Ridge. Kreycik's cellphone was later found inside his vehicle parked at Moller Ranch.

Ground searches occurred during the day on Sunday and Monday. The Alameda County Sheriff's Office on Monday night conducted an aerial search for Kreycik stretching from Interstate 580 down to Highway 84 using aircraft with night vision capabilities, but turned up no signs.

A total of 20 search and rescue teams on foot and e-bikes have also scoured a 50-square-mile area "in an organized and systematic approach," for signs of the father of two, along with using dogs, drones, fixed-wing aircraft and thermal technology.

"It is believed that Kreycik is either incapacitated or not in the general area," officials said, and the case remains a missing person investigation. He had not been located as of press time Wednesday.

Foothill High School served as a staging area over the past few days for PPD and other agencies supporting the coordinated search and rescue effort, including the East Bay Regional Park District Police, California Highway Patrol, and Livermore-Pleasanton Fire Department and its community emergency response team. Local businesses such as Gene's Fine Foods, Porky's Pizza Palace and Pizza Bello have also donated food and water for search teams.

On social media, neighbors have been analyzing park and trail maps for where to expand or deepen their search efforts, and even looking to Kreycik's running habits for clues. Some people also knocked on the doors of nearby homes, making sure Kreycik didn't go seeking help after possibly experiencing dehydration or heat exhaustion.

One user on a Facebook page created by volunteers reviewed some of Kreycik's past runs recorded on a geo tracking app and said, "One thing strikes me is that he's a super fast downhill runner," and suggested paying "more attention to steep downhills and possible skid marks along his route."

Kreycik is described as a white male, with a thin build, brown hair and brown eyes. He was last seen wearing shorts, a watch, socks and grey Saucony sneakers. He is an experienced long-distance runner with no known health conditions.

The East Bay Regional Park District system, including the Pleasanton Ridge, remained open for visitors.

Anybody with information about Kreycik's location is asked to contact the Pleasanton Police Department at 931-5100.