(CBS/AP) TUCSON, Ariz. - The family of an Arizona girl who went missing from her bedroom over the weekend said they will never give up looking for the 6-year-old.
"We appreciate everyone's interest in finding our daughter, Isabel, and thank all the volunteers who have come out to search for her," the family of Isabel Mercedes Celis said in a statement Monday evening in their first public comments. "We love Isabel and will never give up finding her."
Tucson police are trying to determine what happened to Isabel. Her parents say they awoke on Saturday to find her missing. Police said a window was open with the screen pushed aside.
Since Saturday, investigators and volunteers fanned across Isabel's neighborhood and an area landfill searching for clues. Volunteers posted fliers with a photo of Isabel -- about 4 feet tall with brown hair and hazel eyes -- holding a school award.
Her parents, identified by friends as Becky and Sergio Celis, told investigators they last saw the first-grader at 11 p.m. Friday. Her mother, a nurse, was at work Saturday when her father went to wake her at 8 a.m. and discovered her missing, police said.
Police call the case a "suspicious disappearance/possible abduction."
"We're not ruling anything out of the investigation at this point because we really need to keep our mind open about all the information that's been brought to us," Police Chief Roberto Villasenor said.
Officers have been interviewing sex offenders in the area -- a practice that has become standard in all abduction investigations.
On Monday, FBI dogs -- one that can find human remains and the other used for search and rescue -- went through the family's home and turned up information that required a follow-up, but police declined to say what that was.
The family said in the statement that they are fully cooperating with authorities.
Experts say abduction from the home is relatively rare, with just over 18 children taken each year.
"It's unusual, but it's not unprecedented," said Ernie Allen, president of the National Center for Missing and Exploited Children, which is involved in the search.
CBS Affiliate KOLD reports Tucson residents are coming together to contribute to the search. Family friends and employees of Tucson Medical Center - where Isabel's mother is a nurse - started a mass campaign to distribute flyers.
The volunteers set up a tent in a parking lot across from the police command post, distributing flyers and collecting donations. Dozens of people stopped by to pick up stacks of flyers to distribute in their neighborhoods; Local businesses stepped up as well. .
"It hits home, it really hits home," one mother told KOLD correspondent Sonu Wasu.
New protocols for investigating missing children
Each year, 58,000 children are abducted by strangers and released, according to the most recent statistics. Of those, 115 were "stereotypical" kidnappings carried out by strangers who either killed the children or held them for ransom. And 16 percent of those were taken from home.
Nearly three quarters of the victims are girls, and 38 percent of them are 12 to 14. At 24 percent, the second largest victimized group is the one Isabel belongs to: girls ages 6 to 11.
When 12-year-old Polly Klaas disappeared during a slumber party in 1993 in California and was strangled by a man with a long criminal record, there were no police protocols, said her father, Marc Klaas.
"Every time a child would disappear, they would invent that wheel all over again," said Klaas, who travels the country speaking about child abduction. "Now almost every agency in America has some handle on how to launch a missing child investigation."