FILE - This undated file photo provided by the Tucson Police Department shows Isabel Mercedes Celis, 6, who has been missing since April 21, 2012 from he Tucson, Ariz., home. Dozens of police officers knocked on doors in a Tucson neighborhood Wednesday Jan. 15, 2014, in hopes of finding new information in an investigation of Celis, who was abducted more than 18 months ago. AP Photo/Tucson Police Department, file A door-to-door effort launched this week in the case of a Tucson girl who disappeared from her bedroom more than 18 months ago has yielded some possible tips, police said Saturday Officers expect to finish talking to residents Saturday in the area where 6-year-old Isabel Mercedes Celis lived, Sgt. Pete Dugan said. Police received several phone calls within the last few days and were trying to figure out if any hold new information, he said. "Now what's happening is behind closed doors, investigators have to weed through those calls," Dugan said. He declined to say what the calls were about because the investigation was still active. Since Wednesday, more than 50 officers have gone out daily to more than 350 houses and apartment units. According to Dugan, investigators spoke with people new to the area as well as those who were around when the child first went missing. "Lot of times people won't call 911 with a little piece of information," Dugan said. Authorities have been searching for the girl since her father reported her missing in April 2012. Dugan says the neighborhood canvass was not being conducted because of any new lead. It had been planned for months, Dugan said. "We are just letting the public know this case did not go away," he said. Messages left for the girl's parents were not immediately returned. But the girl's mother, Rebecca Celis, said earlier in the week she was pleased police were renewing efforts. "We are happy they are trying to get new eyes on the case," the mother said. Family members have said they last saw her in her bedroom the night before she vanished. A window was later found open with the screen pushed aside. A neighbor said she heard her dogs barking and male voices outside her bedroom window around 6:30 a.m. on the day the girl was reported missing. The neighbor said there were no sounds that indicated a struggle. Police have declined to say whether the child is believed to still be alive. They believe the girl was abducted but haven't concluded whether it was done by a stranger or someone known to the family. Still, police said whoever was responsible for the abduction had knowledge of the home's layout. About a month after the child's disappearance, police revealed that her father, Sergio Celis, had been barred from have contact with the girl's two older brothers, but they did not say why. In the weeks after the disappearance, authorities searched for the child in a 3-square-mile area around her home, including ponds, dry streambeds and empty houses. They also searched her house, but records of that search have been sealed by a judge.