Tucson, Arizona (CNN) -- The parents of missing 6-year-old Isabel Mercedes Celis pleaded for her safe return Wednesday after police said they had scaled back their search for her.
"Please, please -- to the person or persons who have Isa, tell us your demands," said her father, Sergio Celis. "Tell us what you want. We will do anything for her."
Isabel was reported missing from her family's home Saturday morning. She was last seen by family members when she went to bed at 11 p.m. Friday, and a screen was found removed from one of the home's windows, according to Tucson police.
Celis and his wife, Becky, thanked volunteers who have been taking part in the search. Addressing his daughter directly, he said, "We miss you so much, and we will never give up. We will never give up looking for you."
Celis said the couple would increase the current $6,000 reward offered to help produce a break in the case. Tucson Police Chief Roberto Villaseñor later told reporters the offer had been raised to $30,000.
Tucson authorities have described the child's disappearance as suspicious, but have not identified any suspects in Isabel's case or indicated what they believe may have happened to her.
"We have not received a ransom note of any kind, but of course we have to take into consideration the possibility of an abduction," Villaseñor said Wednesday afternoon. "But we also have to look at it from the viewpoint that maybe it's not, and we have to look at other things."
He called the disappearance "a complex case," and said police have "limited information" so far.
Police have methodically searched a 3-mile radius around the family's home and a local landfill. Investigators had wrapped up their search of the family's home and turned it back over to the family, but "I don't think they're interested in coming back," the chief said.
Investigators are still pursuing more than 300 tips, but the number of officers committed to the search is being pared back.
"It doesn't mean we've abandoned the search," he said earlier Wednesday. "We have just scaled back some of our personnel. We have accomplished the majority of the search of the sites we wanted to visit. We are now concentrating our search on maybe some focal points where we are hoping we'll have a little bit more success."
HLN's Natisha Lance contributed to this report.