Jan. 21 Update: Since this story aired, there have been updates in the case. Click here to read the latest.

(NewsNation Now) — It’s been nearly three months since 18-year-old Brendan Santo vanished while visiting friends in East Lansing, Michigan.

On the cold and icy campus of Michigan State University, a fiery hope keeps loved ones searching for answers.

“The challenge for us is going to bed every night not knowing where your son is,” Brendan’s father, Brad Santo, said. “It’s tough.”

The Santo family has been returning to the Michigan State campus nearly every day since last October, retracing steps and playing out theories in an effort to put the missing pieces of a puzzle together.

“I’ve tried climbing the wire over there,” Santo’s father said of trying to retrace his son’s steps. “It just doesn’t seem, he’s obviously much younger than I am, it is just not an easy, not an easy thing to get over.”

Santo’s father said he has walked these streets hundreds of times — for hundreds of miles — since his wife received the call on Oct. 30 relaying the news that their son had been missing from MSU’s campus for 16 hours.

The family has tried “calling hospitals, you know everything, everything that a parent would go through.”

“We didn’t know what to think,” he said. “That is just out of character, out of character for him”

Santo is a freshman at Grand Valley State University, a school about an hour’s drive to the west.

He made the trip to MSU last October to visit friends during Halloween weekend and attend one of the biggest college football games of the season.

“It was the evening before the big football game, MSU versus (the University of Michigan). It was Halloween weekend and it was really coming out of COVID a little bit, at the time when there were some of the regulations being relaxed,” Chris Rozman, an inspector with MSU Police and Public Safety, said.

In the midst of a celebratory scene on the night of Oct. 29, Santo left a gathering of friends at a residence hall around midnight.

Data from his phone shows he was planning to meet up with another friend who was close by.

Santo was in the area just outside of the residence hall when the data signals and all sightings of the college freshman stopped.

“We know he didn’t run away, we are pretty confident in that,” Santo’s father said. “So it is either one of three things: He is either in the river, someone took him or something else happened.”

Scouring land and water for clues, hundreds of professional investigators and volunteers have joined the effort to help search for Brendan Santo.

“At this time, our investigation has been reviewed by our local, state and federal partners and we still do not have any reason to believe that any foul play is involved and that is where the case stands right now,” Rozman said.

Police and dive teams from more than five counties in the state focused their efforts on a river in the same vicinity where Santo’s cellphone was last detected.

“Early in the investigation, we utilized multiple K9 teams as part of our search effort and we did have multiple cadaver dogs indicate on the Red Cedar River in the area where Brendan was last seen,” Rozman said.

“I just don’t know because those dogs are not specific to a person, it is just to a body, and I know other people have fallen in the river, so that scent can hold on forever,” Santo’s father said.

Part of the river’s edge where authorities are searching has a steep drop-off from the sidewalk. One theory is that Santo mistakenly fell down the incline and into the water. But after months of searching, not one piece of evidence has been uncovered.

“There is so much down there that if you fell down this embankment it would be difficult not to get caught somehow,” Santo’s father said. “You would think that his hat would have blown off if he fell down one of the banks.”

“It is always important, when we do our jobs, we carry a level of hope and we do not make any assumptions, and that is what we are doing, and we are committed to bringing Brendan home and resolving this case,” Rozman said.

Santo’s family is asking the nation to be on the lookout, pleading for any additional information from the local community.

“It is so frustrating that someone hasn’t come forward,” Santo’s father said. “Police need that tip, that information to go on to follow something.”

Brad Santo describes his son as independent and funny, a fan of sports and close with family.

Since Santo’s disappearance, his father has been taking time off work and focusing his efforts full-time on the search.

To stay employed, he’ll soon be required to return to his job.

For now, though, he is taking it one day at a time, saying he will never stop searching for his son.

“Obviously the longer it goes on, the tougher that it is, but we’re trying to hold out hope,” Brad Santo said. “You know, that is our choice.”

Anyone who sees or hears from Santo should call the MSUPD tip line at 844-996-7873 or you can email tips@police.msu.edu.

You can also contact Crime Stoppers of Mid-Michigan at 517-483-7867.