this half hour with a mystery involving that 15-year-old teenager, a cheerleader, named gabrielle swainson. She vanished from her home in south carolina with no trace. Her family says he's not a... See More
this half hour with a mystery involving that 15-year-old teenager, a cheerleader, named gabrielle swainson. She vanished from her home in south carolina with no trace. Her family says he's not a runaway. Now, the fbi's on the case. Abc's john schriffen is here with the story. John, good morning to you. Reporter: Dan, good morning. The family of the missing girl has hired a private investigator to piece together the last moments gabrielle was seen alive. Her mother and authorities running out of options. Now, also turning to the public for help. This morning, police are baffled. How did 15-year-old gabrielle swainson disappear, seemingly without a trace? I don't know what has happened. I don't know how it happened. And this is really a nightmare. It really is. This is the worst situation that a parent could be in. Reporter: It happened one week ago. Gabrielle's mother, elvia left for work at 3:30 a.M. Saturday morning. The high school cheerleader was asleep in her bed, wearing pink and black pajamas. When elvia returned four hours later, gabrielle's bed was empty. She was gone. I grabbed my phone. And I started calling her number. The number rang a couple of times. Then, it stopped. Then, I called it back immediately again. And it went straight to voicemail. Reporter: Her cell phone was gone. But more alarming, her purse and wallet were left behind, suggesting her disappearance was not voluntary. Her pocketbook was there, with her charger in it for her phone. And all the ingredients of her purse. Her wallet, her credit card, even is still there. Reporter: Her mother has hired a private investigator, who says there's been no activity on her phone since the disappearance. Police have not been said whether they've been able to locate the phone's signal. But now, the fbi has joined the search. There's roughly 100 stranger abductions of children a year. So, statistically the idea that a complete stranger abducted her is extremely low. Reporter: The community has rallied behind the family. Passing out flyers. Raising $6,000 for a reward. This past thursday was supposed to be the high school sophomore's first day of school. The community of columbia, south carolina, rallying behind the search, with billboards going up yesterday. And thousands monitoring the facebook page help us find gabby. With no leads right now, police hope the new efforts will help.
This transcript has been automatically generated and may not be 100% accurate.