BROWARD COUNTY, Fla. -- "America's Most Wanted" is getting involved to help solve the murder of a 17-year-old girl whose body was found floating in a plastic bag in a canal off Alligator Alley three years ago.

A representative from the nation's No. 1 TV crime-fighting show was on hand Tuesday, along with Florida Highway Patrol officials, philanthropist Joel Mamanna and the father of Marissa Karp, at a news conference unveiling a billboard announcing the $100,000 reward for information leading to the arrest and conviction of the person responsible for her murder. It would have been her 21st birthday.

"Hopefully, this money can be used in a positive way," said Mamanna, who is offering the reward money. "We can find this piece of trash that did this to this young girl, and this money can make him feel the pain that he deserves."

A local fisherman discovered Karp's body on Aug. 19, 2002, about two miles west of the Miccosukee Mobil gas station just inside the Collier County line. A medical examiner determined that she had been shot to death.

Investigators learned that on April 17, 2002, Karp was reported as a runaway from the Department of Children & Families. Although she had not been seen since, investigators said Karp maintained phone contact with family and friends through early August 2002.

Police believe she was killed before her body was dumped in the canal, but they said they are not sure if her killer knew her.

"She was a great kid," Karp's father, Gary Karp, told Local 10's Yvonne Nava. "She wanted to be a teacher. She didn't deserve to end up like this."

The investigation is ongoing, but police have said that leads are dwindling.

Now, "America's Most Wanted" is hoping to make a difference by attaching its name to the investigation.

The show's host, John Walsh, suffered his own tragedy when his 6-year-old son's remains were found 16 days after Adam Walsh was abducted from a Florida shopping mall on July 27, 1981.

Anyone with information about the crime is asked to call Broward Crime Stoppers at (954) 493-TIPS or "America's Most Wanted" at (800) CRIME-TV.