Jessica Ridgeway was last seen Friday after leaving home to meet friends at a park so they could walk to school together in the Denver suburb of Westminster.
Westminster police spokesman Trevor Materasso said at a news conference that police believe the girl was abducted by an unknown suspect. He said the focus of the case is not on her parents, who are cooperating.
"We're confident they are not involved in Jessica's disappearance," Materasso said.
Authorities are pursuing tips from five other states, including Maine, where a woman reported seeing a girl resembling Jessica Ridgeway on Sunday. That tip and others from Maryland, Texas, Nevada and Wyoming are among the hundreds of bits of information that have been passed on to Westminster investigators, Materasso said.
He didn't release details but earlier in the day said police were looking at whether there's a link between Jessica's disappearance and the Monday abduction of a girl in Cody, Wyo. - about 500 miles away.
In that case, a man lured an 11-year-old girl into a sport utility vehicle saying he needed help finding his puppy. She was released about four hours later and found by hunters. Police there say they're looking for a white man between 55 and 60 years old with short, strawberry blond or white hair and a neatly trimmed mustache.
Two days after Jessica disappeared, her backpack was found on a sidewalk in a neighborhood about six miles north of her home. Police won't discuss what was found inside the bag or the results of testing done on it.
The same day the backpack was found, a woman reported seeing a girl who looked like Jessica in a blue Buick station wagon with Colorado license plates in Dexter, Maine - 2,000 miles away.
Authorities don't know if it really was Jessica spotted in the town of 5,000 people, but they've issued a statewide alert for officers to stop a blue Buick station wagon with Colorado plates if they see one, Dexter police Sgt. Alan Grinnell said. So far, none have been stopped. The car's license plate number wasn't known.
Materasso said searchers were scouring Jessica's neighborhood and divers were searching ponds as a "precautionary measure" to see if they could be ruled out as having a connection to her disappearance. Police also have isolated landfill garbage collected around the time of the girl's disappearance but will search through it only if their investigation points them in that direction, he said.
Police have revealed little about their investigation and have instead tried to keep the focus on Jessica. They've asked the public to study her face in various photos they've released showing her with and without glasses. They're also encouraging people to keep tweeting about her in the hopes that will develop new leads.
Materasso told KOA-AM that investigators are checking out people identified by tips and there are no persons of interest yet.
"We know she's out there, and we want to bring her home," Materasso told the station.
Jessica's mother, Sarah Ridgeway of Westminster, and her father, Jeremiah Bryant of Independence, Mo., issued their first public call for help finding their daughter in a television interview Tuesday.
"I want her to come walking back through that door," Sarah Ridgeway said. "I need her to come walking back through that door."