PLEASANTON (KPIX) — After five days of extensive searches for missing ultramarathon runner Philip Kreycik, the Alameda County Sheriffs Department is calling off its search efforts.

Wednesday was the last day search and rescue crews spread out across Pleasanton Ridge Regional Park to look for the 37-year-old runner who has been missing since Saturday.

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Alameda County Sheriff’s Sgt. Ray Kelly said after hundreds of search crews canvassed more than 50 square miles, there is still no sign of Kreycik – leading investigators to explore other possibilities.

“First scenario is he is somewhere up in this ridge area, this park open space area. Second scenario is that he parked his vehicle at that trailhead and he is somewhere else and that’s why our investigation is on going looking at all possibilities,” says Pleasanton Police Lt. Erik Silacci.

While police investigators have not gone so far as to call this a criminal investigation, they are treating this as a missing person case. Detectives have interviewed friends and family trying to piece together the timeline leading up to Kreycik’s disappearance.

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Kreycik told his wife on Saturday morning he was planning to go for an hour long run at Pleasanton Ridge. When he didn’t return as planned, she called police. Officers found the car they believe Kreycik was driving at the Moller Ranch staging area on the edge of the park. His cell phone was inside, programmed with an 8-mile running route. Despite searches on the ground and the air, detectives say there is no evidence he ever entered the park for the planned run.

“We are perplexed as to why we haven’t found Philip yet, but we’ll keep working it,” said Kelly. He added search and rescue crews could be called out reactively if new evidence points to Kreycik being in the park that day.

Friends and family of Kreycik have organized unofficial daily searches with volunteers. In a social media post late Wednesday night, the group says they plan to search the neighborhoods below the park, thinking maybe Kreycik got disoriented in the heat on Saturday afternoon and came down toward the houses for help.

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If that doesn’t turn up any signs of him, the volunteer group says they will end their formal search efforts as well.