Holly's cousin, country music singer Whitney Duncan, tried to provide searchers with some hope on Twitter.
"I can't thank y'all enough for all the efforts to find holly. Keep it up until she is home with us," she said.
Bobo's father said Thursday that he believed the man may have been someone who knew the young nursing student and knew the family's routines.
"It might have been somebody close, somebody that kind of knew our routine and when I left and when she left [his wife] and when my daughter left to go to school, is what I got in my mind," Dana Bobo said. "But I don't know what for sure."
Police said they are considering the same theory.
"It's very possible that he could have known her, could have known her daily routine. We're following up on everything we possibly can," said Decatur County Sheriff Roy Wyatt.
"As long as we keep our faith that she is alive," said Wyatt, the search will continue.
The army of volunteers searched for Bobo on foot, on horseback and using ATVS.
"Holly I love you so much. Please try to get home to us and if anybody knows anything about her please, please help us find her," said Karen Bobo, Holly's mother.
Pink ribbons and pictures of Holly Bobo are posted all over the town of Parsons, a close-knit community of 2,500 people.
"If this was my daughter, I'd want everybody doing the exact same thing for her," one volunteer said.
"She was a really good person who I never would have dreamed this would happen to," said friend Felicia Tegethoff. "She didn't need it to happen to her, she was doing something with her life, you know."
Bobo is 5-feet-3 and weighs 110 pounds. She was last seen wearing a pink shirt and blue jeans.