PLEASANTON (KPIX) — On the fifth day of searching a Pleasanton regional park for missing Berkeley runner Phillip Kreycik, frustration is mounting among authorities.

“We are definitely at a point where we are a little perplexed as to why we haven’t found Phillip yet. We’ll keep working. Where there’s hope, we’ll keep working,” said Alameda County Sheriff’s Sgt. Ray Kelly.

READ MORE: San Jose Police: Smash-And-Grab Thieves Target Eastridge Mall Jewelry Store; 4 Suspects Sought

Early Wednesday morning, crews focused on a new area of the park where a family member heard something overnight.

According to a “Finding Philip Kreycik’” Facebook page, the family member could hear cries for help on the Sunol side of the regional park around 1 a.m. The yells were apparently coming from a canyon in the area.

At around 5:30 a.m. Wednesday, a post office parking lot in Sunol was the gathering spot for experienced hikers to go up in the hills to follow this possible lead.

Unfortunately, there were no reported developments during Wednesday’s activity after that promising lead, according to sheriff’s investigators.

Hundreds of volunteers and law enforcement have been searching the park since the weekend, looking for any sign of the 37-year-old Berkeley resident, who never turned up after going for a jog Saturday morning at the park.

Authorities said the search is unprecedented in scope, with 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.

Wednesday morning, e-bikers and mountain bikers were being asked to ride trails in the southern half of the park as the focus shifts toward the area where the sounds were heard.

“We’re entering day five. Obviously we are concerned about lack of water, shelter,” said Pleasanton Police Lt. Erik Silacci during an update on the search late Wednesday morning.

Authorities have an Alameda County drone team en route to the area to deploy drones and continue the search.

READ MORE: Man Found Fatally Shot Near Park In Hayward

Crews are also going over already searched terrain to make sure they don’t miss anything.

Although Wednesday’s search operations were scaling down, the investigation is picking up. Every detective in the Pleasanton Police Department is involved. They are currently going through Kreycik’s timeline on Saturday from the time he left his house to when he arrived to Pleasanton.

“Can confirm that we do have him dropping off a package at a parcel store in Oakland,” said Silacci.

The lieutenant said there wasn’t anything raising a red flag so far, but authorities want to retrace his steps thoroughly.

“We have yet to identify an eyewitness who saw him on that trail. And that’s why we’re asking for the public’s help,” explained Silacci. “If you saw Phillip or even if you were on that trail that morning or that afternoon please contact the Pleasanton Police Department.”

The huge effort that includes 59 search and rescue crews from as far away as Santa Barbara continued to scour Pleasanton Ridge Regional Park on Wednesday with no new signs of the missing jogger.

“The searchers all have GPS units on them. Those GPS units broadcast live via their phones to our map here. You can see some of these dots are moving; those are searchers we have in the field live as we speak,” said Liam Anderson with Marin County Search and Rescue. “We have covered the vast majority of high probability linear features throughout the search area. We’ve also focused on the linear features, drainages, ridge lines; features that traditionally attract lost and missing people.”

As far as East Bay authorities go, the massive search operation will wrap up Wednesday night after another pass of drones and aircraft using thermal imagery.

“Our own people out searching, we can see them from the camera. We haven’t seen that human form, that shape. We aren’t seeing those images,” said Kelly.

While Pleasanton police and the Alameda County Sheriff’s Office will switch to a more reactive approach for their investigation after the massive search over the past five days, The volunteers who have been part of the search effort tell KPIX they will continue their efforts.

MORE NEWS: Guard Indicted for Sexual Assault of Inmates at San Joaquin County Jail

Andria Borba and Justin Andrews contributed to this story.