BURLINGTON Twp., N.J. (CBS) — Even though the police search has ended at Burlington Township Park where Sarah Townsend’s car was located Monday, area residents — including Bill Welch, father of the missing 18-year-old girl’s boyfriend Matt Welch — continue to comb the area looking for her.

The mother of Sarah Townsend once again made an emotional plea for her safe return, and with each passing second the mystery surrounding Sarah’s disappearance grows deeper.

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“In my heart I feel somebody knows something or somebody saw something and they need to step up,” said Laurie Townsend.

Laurie believes that her daughter Sarah is out there somewhere, and she is doing everything she can to find her, including accepting the use of an interstate advertising billboard on Route 206 in Columbus, NJ to put up a life-size poster with Sarah’s picture and a $10,000 reward. (See related story)

“They’re volunteering donating the use of the billboard free of charge. I want to thank them. The only thing we have to do is pay the printing fee.”

Investigators confirmed Wednesday that when Sarah’s car was found early Monday morning at Sherman’s Pond in Burlington Township, the engine was still running and the driver’s door was open.

Officials have stated that they do no suspect foul play, but public safety director Walt Corter says they were concerned from the very beginning that she may try to harm herself.

Three days of searches by hundreds of people have not produced a trace of Townsend.

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Police say a bloodhound, employed Wednesday, tracked a scent to the woods behind a neighborhood on nearby Neck Road, but still nothing.

“We grow more concerned with each passing day,” said Corter.

Townsend’s mother doesn’t believe her daughter would try to harm herself.  She says Sarah was in good spirits days before she disappeared.

“Sarah is going to two proms this year. Before this happened she was trying on dresses.  That’s not a child that’s planning to run away, in my opinion.”

Allentown High School, where Sarah attended despite living in Florence Township, is planning on holding a vigil for Sarah and her family at 8 p.m. Monday night at the football field. Any money raised during the event will go to the Townsend family.

If you have any information, Burlington Township Police can be reached at 609-386-2019.

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Reported by Robin Rieger, CBS 3; John McDevitt, KYW Newsradio 1060