Eileen Auch Law, a private investigator who has been assisting Sharpless's distraught family, said the investigation has been frustrating but she remains optimistic that Sharpless will be found.
"There is absolutely no evidence to the contrary," she said.
Crystal Johns, a longtime friend of Sharpless and the last person to see her, told investigators that the pair had been invited to Green's Main Line home after meeting him at a Philadelphia nightclub. She said Sharpless apparently had too much to drink, and they were asked to leave.
Once outside, Johns suggested that Sharpless should not drive, the two argued, and Sharpless drove off, stranding Johns, who had to call a relative for a ride home. Johns called Sharpless' behavior unusual.
Even more uncharacteristic was the fact that Sharpless had gone out for a night on the town, her mother said. She said her daughter had been working tirelessly as a nurse to provide for her daughter, who was 12 when Sharpless disappeared.
Knebel said she and her husband, Peter Knebel, were eager to give Sharpless some relaxation time and had offered to watch their granddaughter.
Among many adversities her daughter had overcome, Knebel said she had finally found a successful treatment for her bipolar disorder - medication that should not have been combined with alcohol. Even worse, Sharpless had worked a midnight shift the night before at Lancaster General Hospital, exacerbating the mix with a lack of sleep.
Police said Sharpless' cellphone has not been used since she sent a text message to her daughter a few hours before leaving the party, urging her to get a good night's sleep. Her credit cards have also not been used, and her car was only spotted once, by a machine that records license-plate numbers on Sept. 8, 2009, in Camden.
That same month, 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.
Law, who has set up a Sharpless Facebook page and a website - www.MissingToniSharpless.com - to generate leads, has theorized that Sharpless's impaired condition could have made her vulnerable to a drug or prostitution ring.
She said the recent rerun on the Investigation Discovery network of an episode of "Disappeared" that featured Sharpless, resulted in several possible sightings in the New Castle, De., area.
"Someone knows something more than what has been presented: I pray they will come forward," said Law.
Anyone with information should call West Brandywine Township police at 610-380-8201 or Law at 610-388-1776. Knebel also suggested that if someone thinks they see her daughter, they should "take a picture with a cellphone."
Contact staff writer Kathleen Brady Shea at 610-696-3815, firstname.lastname@example.org, or @brandywinebits on Twitter. Read her blog, "Chester County Inbox," at www.philly.com/chescoinbox.