Mystery lingers about a Chester County nurse and mother who left a party at a 76er player's home in Penn Valley on Aug. 23, 2009, and vanished. Now, a TV show is taking up the case - and its dearth of clues.

An episode of Disappeared on the Investigation Discovery network at 9 p.m. Monday will explore the mystery of Toni Lee Sharpless, who was 29 when she planned a night on the town and never returned.

"I just hope this reaches the right people, and our daughter is brought home to us," said Sharpless' mother, Donna S. Knebel.

Lower Merion Township Police Lt. Frank Higgins called the case highly unusual. Not only did Sharpless disappear, but her car has not been found, and her cell phone and credit cards have not been used.

"At this point, whatever you can do to generate interest is a good thing," Higgins said of the TV episode.

Elizabeth Fischer, executive producer of the show, said Sharpless' ability to overcome hardships and the myriad unanswered questions her disappearance generated made the case appealing.

"We thought, if our show could help to shed light on some aspect of the case, that would be a tremendous outcome," she said.

The production crew visited the area for a week in late September, interviewing police, friends, relatives, and associates to learn Sharpless' background.

Sharpless and a longtime friend, Crystal Johns, met Sixers guard Willie Green at a Philadelphia nightclub and were invited to his Main Line house. After a "verbal dispute" with Sharpless, Green asked them to leave his residence about 5 a.m. Police have said Green had nothing to do with Sharpless' disappearance.

Johns, who called Sharpless' behavior uncharacteristic, said she tried to persuade her not to drive and ended up being ordered out of the car. Johns said she had to call a relative to rescue her when Sharpless failed to return.

Relatives said Sharpless, who had worked a midnight shift the night before at Lancaster General Hospital, was sleep-deprived. Mixing alcohol with medication she took for her bipolar disorder would have exacerbated her impairment, they said.

Since then, her car - a black 2002 four-door Pontiac Grand Prix with Pennsylvania tag DND-7772 - has been recorded once, by a police license-plate reader on Sept. 8, 2009, in Camden.

"That's the only substantive clue we've had," Higgins said.

Sharpless' cell phone has not been used since she sent a text message to her daughter, who was 12 at the time, urging her to get a good night's sleep a few hours before leaving Green's, police said.

Sharpless had moved in with her parents, Donna and Peter Knebel, in West Brandywine Township during nursing school so they could help care for her daughter.

The Knebels said their daughter had overcome much adversity.

Though Sharpless became a mother at 17, she graduated with honors from Coatesville High School, her parents said. A job as a certified nursing assistant inspired her to pay her way through Brandywine Hospital's nursing school. She graduated in 2007, began working at Lancaster General, and was planning to seek a master's degree.

Her parents said she sought medical help periodically for mood swings and was finally diagnosed in 2004 with bipolar disorder.

The experience has turned the Knebels into tireless advocates who are grateful to the many people who have helped them.

In September 2009, Texas EquuSearch, a nonprofit search-and-recovery firm, used sonar to see whether Sharpless had accidentally driven into the Schuylkill near Flat Rock Park in Gladwyne. Eleven submerged vehicles were found; none belonged to Sharpless.

Eileen Auch Law, a private investigator who has worked the case free, said Sharpless may have run out of gas or gotten lost. In her impaired condition, she would have been vulnerable to exploitation, perhaps by a drug or prostitution ring, Law said.

Law set up a Sharpless Facebook page and a Web site - www.MissingToniSharpless.com - to generate leads.

"I pray that the airing of this show will bring answers with it," she said.

Anyone with information is asked to call Lower Merion detectives at 610-649-1000 or Law at 610-388-1776.

Contact staff writer Kathleen Brady Shea at 610-696-3815 or kbrady@phillynews.com.