"Whoever has her, I know you're watching," Crystal told "Good Morning America." "She ain't done nothing wrong. Please bring her back."
Haleigh, whose parents do not live together, disappeared from the Satsuma, Fla., home of her father, Ronald Cummings, Tuesday. He reported her missing in an desperate 911 call.
"I just got home from work and my 5-year-old daughter is gone," he told a dispatcher. "If I find whoever has my daughter before you all do, I'm killing them. I don't care if I spend the rest of my life in prison."
There are 44 registered sex offenders within a five-mile radius of the home.
Ronald Cummings had left Haleigh and her 3-year-old brother in the care of his 17-year-old girlfriend, Misty Croslin.
"She was sleeping right next to me," Croslin told the Palatka Daily News. "I can't believe I didn't hear anything."
Ronald Cummings told police that when he returned from work early Tuesday morning, the back door was propped open and Haleigh was gone.
"Somebody came in my back door, broke into my home and stole my daughter," he said.
On Wednesday night friends and neighbors held a small vigil for the little girl. The search effort has also attracted several volunteer groups that could join the search today, according to The Associated Press.
"I don't know why somebody would take her," the mother said. "I'm scared for her. She is probably scared and cold and hungry."
The Associated Press contributed to this report.