CHICAGO - Police have stepped up their search for a missing pharmaceutical company sales representative after finding the 28-year-old woman's car near an abandoned building.

Nailah Franklin was last heard from Tuesday, when she sent an uncharacteristically vague text message to friends and family saying that she was having dinner and that she'd call later. She never did.

Franklin's sister, Lehia Franklin Acox, said the family is trying to stay positive as police search the 2005 Chevrolet Impala for clues that could shed light on her disappearance.

Being positive "is our only option," Acox said Saturday afternoon ahead of a prayer vigil that evening.

"We're all just trying to keep our spirits up, but it's a challenge," she said.

"This is really taking a toll on us, with every day that passes. We're not sleeping well, we're not eating well," she said.

When Franklin didn't turn up for an important meeting Wednesday morning with her boss at Eli Lilly and Co., where she's a pharmaceutical sales representative, co-workers called family, and family called police. Eli Lilly is based in Indianapolis. Franklin's sales territory covered Chicago's suburbs, her sister said.

Acox said it's unusual for Franklin not to contact her friends or family, leading them all to fear that she didn't leave willingly. Last week, Franklin filed a police report about threatening phone calls she'd received, but she declined to file an order of protection against the alleged offender, a man she'd once dated.

Franklin's car, along with some personal items, was found Friday night near an abandoned building in Hammond, Ind., said Chicago Police spokeswoman Monique Bond. She said the car is being transported to Chicago for forensic and evidence processing.

Several jurisdictions, including Chicago, Hammond, Ind., and the Cook County Sheriff's department are searching for Franklin, Bond said. Divers have also been involved in the search.

Acox said the discovery of the car was heartening because it could yield some clue to Franklin's whereabouts, but "on the other hand, it's still maddening because we do not have (her) back with us."