Isabel Celis has been missing for nearly two years.
The little girl, who was six years old at the time, was last seen the night of April 20, 2012, when her parents tucked in her to bed at their Tucson home.
By morning, Isabel was gone.
Police have yet to crack the case – but they're trying.
"A missing child, of course, hits home, and we're going to do everything we can to make sure we've exhausted all means possible," said Sgt. Pete Dugan with the Tucson Police Department.
On Wednesday, about 50 officers and several detectives went door-to-door – talking with neighbors - in an effort to generate new leads.
"We're trying to see if anybody has even the smallest piece of information," said Dugan. "It may seem insignificant to people, but it could be huge compared to what we already have."
This is the second time since Isabel vanished that police have combed the area – spanning a half-mile radius from the Celis home near Van Buren and 12th streets – and it's a effort welcomed by Isabel's mother.
"It's new eyes; it's fresh eyes," said Rebecca Celis. "What might have been missed the last time when they were canvassing can be easily found this time."
Despite the passage of time, Rebecca Celis said she has hope she'll see her daughter again.
"My daughter didn't just disappear into thin air," she said. "Somebody knows something, and that's what they need to find; we need to find that person. That's going to be her guardian angel - the person who has that information is going to bring Isabel home."
Police hope to hit about 400 homes in the neighborhood this week.
They'll be knocking on doors from noon to 10 p.m. through Saturday.
Copyright 2014 CBS 5 (KPHO Broadcasting Corporation). All rights reserved.
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