(NEW YORK) -- The father of 16-year-old Kayla Campbell, who was last seen three days ago at her North Carolina home, tells ABC News he's more optimistic today that his daughter is alive.
"The authorities have jumped on everything and are doing a great job," said Robert Campbell. "It's been very hard, but my family is staying strong."
On Monday, police located Kayla's cellphone, backpack, shoes and bicycle in a wooded area near her home in Mint Hill, N.C., a suburb of Charlotte.
Kayla was last seen Sunday afternoon when she left home for a bike ride, something that was not out of the ordinary. Her parents told her to return home by 5:15 p.m. when it starts to get dark, but she did not.
"We called her at 5:20 p.m., and she said she was close-by," said the girl's father. "But we didn't feel like she was telling the truth."
Campbell used location software he had installed on Kayla's phone to track her down.
"We became concerned when the GPS on her phone showed her being in one area and she told us she was in another. She's not great with directions," said Campbell.
When the Campbells called Kayla back, her phone had been turned off, and that's when they notified police.
"At this time, we have no reason to believe there was an abduction," said Mint Hill Police Lt. J.K. Rowell.
Campbell admits he was worried about some relationships Kayla had been forming with people on the Internet.
"We were just dealing with the emotions of a teenager, having to do with some online relationships on a Tumblr page," said Campbell. "These relationships were not healthy."
Tumblr is an online social networking site that allows users to create their own, sometimes private blogs to share personal content.
Campbell wouldn't comment on a news report Monday that Kayla was "battling depression."
"I'm not going to talk about her personal history," he told ABC News.
Mint Hill Police, joined by fire search and rescue personnel, combed the wooded area again on Tuesday, which is located a mile and a half from Kayla's home.
Canines and divers searched a nearby pond and the FBI was on site, helping with the investigation.
Kayla Campbell is approximately 5 feet 6 inches tall, weighs 115 pounds, has long brown hair and blue eyes. Anyone with information on her whereabouts is asked to call Mint Hill Police at 704-545-1085.
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