Celina Cass was last seen at a computer in her house in Stewartstown, near the Canadian border, at about 9 p.m. Monday. She was gone the next morning.
Police in the small town say there's no indication the fifth grader ran away or that someone took her, and there are no signs of a struggle.
Family members are planning to put up signs as far away as Florida and Washington, where Cass has relatives.
But tight-lipped police investigators revealed little about the probe beyond that Wednesday, despite a flurry of activity in and around the three-story house where Celina lives with her mother and stepfather.
Senior Assistant Attorney General Jane Young said it is still being treated as a missing persons case.
"We are still desperately looking for her," Young said.
She wouldn't comment when asked why an Amber Alert was never issued for the girl, even though the FBI said it had enlisted a four- to six-person "child abduction rapid deployment team" to pitch in.
Earlier in the day, state police Sgt. Sheldon Belanger, the lead investigator in the case, said Celina's disappearance did not meet the criteria for an Amber Alert and wasn't considered suspicious.
The Associated Press contributed to this report.