No one has seen or heard from Tina Herrmann, 32; her son, Kody, 11; and a friend, Stephanie Sprang, 41, since last Wednesday.
Investigators were using cadaver dogs to search six specific areas, including the Kokosing Gap trail that runs between Howard and Mount Vernon, 10TV's Tino Ramos reported.
Detectives told 10TV that dogs found a possible piece of evidence located off the trail near state Route 229.
It was a sock that appeared to have been recently placed in the area. Investigators were unsure whether it was connected to the missing people.
A shoe was also found at Foundation Park, but there was no immediate word on whether it belonged to one of the missing people.
SLIDESHOWS: Case Timeline | Tuesday's Search | Park Search | Images From Mount Vernon Neighborhood | Four Missing | Search For Missing People | VIDEO EXTRA: Sheriff David Barber's Nov. 15 News Conference
Part of the search also expanded into Howard, 10TV's Shayla Reaves reported.
A group searching south of Gambier reportedly may have found some evidence, but details on the findings were not released.
Matthew Hoffman, who is accused of kidnapping a fourth person in the case, was expected in court on Tuesday afternoon.
Authorities raided Hoffman's home on Sunday morning and found Sarah Maynard, 13, bound and gagged in the basement, 10TV News reported.
His court appearance was delayed Monday while investigators continued to attempt to question him, but authorities said he is not cooperating with investigators.
Authorities and family members continued to hold out hope on Monday that the three will be found alive.
Optimism remained even after an afternoon news conference in which Knox County Sheriff David Barber offered the grim possibility that three people were dead.
Stephen Thompson, the father of Stephanie Sprang, said Monday that he and his family were still holding out hope that his daughter would be found alive, 10TV's Tanisha Mallett reported.
"I know that that time frame has been long between when they disappeared," Thompson said. "But we have hope that we will see our loved ones soon."
Authorities spent much of Monday searching Foundation Park in Mount Vernon for any sign of the three missing people. Officers and deputies used boats and helicopters to search the area, and investigators were seen leaving with bags of evidence.
Authorities downplayed any discovery on Monday night, saying they found nothing related to the case, Mallett reported.
"Your kids, your mom, me, your whole family, we're all looking for you," Thompson said. "We'll be with you until we find you."
Barber said investigators searched the park because of its proximity to Hoffman's home.
Sarah Maynard is doing well and is with family members, Barber said. He also said the girl is helping investigators, but he would not say whether Hoffman was cooperating.
"Not only is she assisting the investigation, under the circumstances a 13-year-old girl being held captive for four days by a total stranger, I would call her the epitome of bravery," Barber said.
Investigators tracked Hoffman down with the help of a receipt for a tarp that was purchased at a Walmart store in Mount Vernon, Mallett reported.
Investigators were reviewing surveillance footage from inside the store.
Kody A. Maynard is 4 feet, 10 inches tall, weighing 70 pounds, with brown hair and hazel eyes.
Sprang is 5 feet, 3 inches tall, weighing 110 pounds, with blonde hair and green eyes.
Herrmann is 5 feet, 6 inches tall, weighing 122 pounds, with sandy blonde hair and blue eyes.
Anyone with information about the case is asked to contact the Knox County Sheriff's Office at 740-397-3333 or the tip line at 888-363-8477.
Watch 10TV News and refresh 10TV.com for additional information
November 15, 2010:
Mother Of Suspected Kidnapper Says He Is 'Loner'
November 15, 2010: Sheriff: 3 Missing People Could Be Dead
November 15, 2010: Police Block Off Park As Mount Vernon Search Continues
November 15, 2010: Suspected Kidnapper's Past Includes Arson Conviction
November 14, 2010: Missing Girl Found Safe; Man In Custody
November 13, 2010: Search For 4 Grows More Intense
November 13, 2010: Support Growing To Find Missing Family, Friend
November 12, 2010: Search Continues For Missing Women, Children
November 12, 2010: 4 Missing From Knox Co.; Discovery Of Pickup Prompts Kenyon College Lockdown