BREAKING NEWS: Search teams have found the body of a female and say it is missing teenager Kelsey Smith.
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About 240 federal agents, police officers and police academy students were deployed to an area in south Kansas City Wednesday in search of 18-year-old Kelsey Smith, who disappeared four days ago.
Following leads developed from cell phone technology, the investigators are searching the areas south and east of U.S. Route 71 and Missouri Route 150. Law enforcement is asking that no volunteers participate in the search in order to preserve the integrity of any evidence found there.
FBI Special Agent Jeff Lanza told FOX News that a signal from Smith's cell phone was last picked up in the area around 8 p.m. Saturday, roughly one hour after she was abducted. Investigators were conducting a grid search of the 900-acre area.
"Right now we’re just trying to follow up on all the investigative information we have to date," Lanza said. "It’s a needle in a haystack right now."
Searchers are walking shoulder-to-shoulder through the rough terrain of hills and brush looking for clues. The area under scrutiny also leads to a lake.
Overland Park Police spokesman Matt Bregel said the signal was a "ping," which occurs whenever someone receives or sends a phone call. He said the ping in question likely was Smith's family trying to get hold of her.
"This is one of several angles we continue to explore in this case," Bregel said during a press conference. "We are still seeking the person of interest shown in the Target surveillance video, as well as the dark colored pickup truck which was also show in the surveillance video."
Bregel said police have received about 500 leads, 200 of which came in Tuesday night. But, he said, "just because we have received 500 leads, we are still asking to see everything ... we're following up on every lead."
Earlier in the day, Kansas authorities identified via video a dark-colored, mid-1970s model Chevrolet pickup truck as a possible vehicle used in her abduction.
Officials had released a surveillance video that showed a "person of interest" walking in close proximity to Smith while she was shopping, and being possibly the same person that was shown in a video rushing toward her car and forcing her inside.
Police want to question the young, goateed man videotaped leaving the Target store moments before Smith's abduction. He has not been identified and was not being called a suspect, but he might have information about the disappearance of Smith, Overland Park Police Chief John Douglas said.
Smith's parents, Greg and Missy Smith, said Wednesday on "The Early Show" that they do not know the man in the surveillance video.
"None of our immediate family recognize him," Greg Smith told CBS.
The family has launched a Web site, www.findkelsey.com, to get information and pictures about Smith out to the public.
Just before 7 p.m. Saturday, the pickup truck caught on video pulled into the parking lot aisle where Smith had parked about one minute earlier, police said. A man is seen leaving the pickup and going into the Target store Smith had entered.
Smith, who graduated from high school less than two weeks ago, left the store around 7:10 p.m. and put packages into her car when someone ran toward her, police said.
"You see two individuals come together, and there is no separation of those two individuals," Douglas said. "So it is easy to conclude there was some kind of incident at the back of the car. Then the car leaves."
But the tape was "just not detailed enough" and was being enhanced at a forensics lab, Douglas said.
"We see activity," Douglas said of the videotape. "We are moving on the assumption — because the prudent thing to do is to treat this as an abduction — that there was some kind of force involved."
More than 50 detectives and officers from the area, the FBI, Drug Enforcement Agency and others were involved in the case, he said. More than 500 people have volunteered to aid the search.
About two hours after Smith disappeared, her grandparents found her gray 1987 Buick in a parking lot at a mall in suburban Kansas City with her purse and packages still inside.
The Smith family has increased the reward to $30,000 for information leading to their daughter's safe return. Greg Smith, who has been in law enforcement for 16 years, described his daughter as an outgoing young woman who plans to be a veterinarian.
Investigators said they don't know if Smith was picked at random or abducted by someone she knew. But Kelsey Smith's 23-year-old sister, Stevie Hockersmith, said she was sure her sister did not know the man police were seeking.
Wherever Kelsey is, Hockersmith said, she felt sure her sister was putting up a fight.
"He doesn't know what he's in for," she said. "Honestly, she'll raise all hell, and she won't stop. Kelsey won't stop until her body makes her stop basically, until she just can't go on anymore."
Smith is about 5-foot-6-inches tall, weighs about 120 pounds and has long brown hair and brown eyes. She was last seen wearing a pink tank top, black cotton shorts and tennis shoes.
Anyone with any information that may help the investigation is encouraged to call the TIPS hotline at 816-474-8477 or the Overland Park Police at 913-327-5638.
FOX News' Alicia Acuna and The Associated Press contributed to this report.