Margaret Ellen Fox boarded a bus in Burlington City on the morning of June 24, 1974, determined to earn her own money and show her family she was capable of being a responsible young woman.

Her family has not seen Fox in the 45 years since.

On the anniversary of her disappearance, the FBI on Monday announced a reward of up to $25,000 for information leading to the arrest or conviction of the person responsible.

Authorities also released a recording of a phone call made to the Fox family’s South Jersey home — and surreptitiously recorded by the FBI — shortly after the 14-year-old vanished. In the call, purportedly from a man claiming he had Fox in his custody, the caller says “$10,000 might be a lot of bread, but your daughter’s life is the buttered topping.”

Her mother can be heard asking the caller, “Who is this?”

Burlington City Police Chief John Fine said the release of the call was not previously possible because the audio had not been clear. The FBI spent years working with developing technology to enhance the tape for digital release.

Fine said authorities were uncertain whether the caller was the person Fox had set out to meet for a babysitting job on the day she vanished, or whether the caller was someone who was aware of her disappearance and seized on it as an opportunity for financial gain.

After the call, Fine said, there were discussions of delivering the ransom payment the caller demanded, but in the end, no contact was made.

In addition to the enhanced recorded call, the FBI worked in its forensics lab in Quantico, Va., to develop images of how Fox might have aged and what she would look like today to circulate in posters seeking information from the public.

Joseph Denahan, assistant special agent-in-charge of the FBI’s Newark field office, said the offer of a reward shows authorities’ commitment to resolving the case.

“Missing a child is a parent’s worst fear,” Denahan said. “Not knowing what happened to your child is a torture beyond what any of us care to imagine. For 45 years, the Fox family has endured that torture.”

Authorities recognize that there is a possibility Fox is dead, Fine said.

“It is our mission that if this is the case, Margaret receives a proper burial,” he said. “The Fox family can make closure, receive the answers that they deserve, and our community can begin to heal.”

Burlington County Prosecutor Scott Coffina said good police work had solved many a cold case.

“We owe it to her and to her family to get answers and resolve the case,” he said.

Fox was in eighth grade at St. Paul School in Burlington when she and her cousin, Lynn Parks, sought babysitting work by placing a classified ad in a local newspaper, with a phone number.

A man who identified himself as John Marshall responded that he had a 5-year-old son, a backyard swimming pool, and a swing set at his Mount Holly residence.

Parks’ parents would not give her permission to go to Marshall’s home, so she gave Fox the man’s contact information. When Fox called him, the man said he would pay her $40 to babysit the child for four hours a day, five days a week, and that he would meet her at the bus stop at Mill and High Streets on June 24.

Authorities traced the phone call to a phone booth at a supermarket in Lumberton, according to the FBI.

Fox left a note for her parents detailing where she was going before she headed to High and Broad Streets for an interview with the man. She went with one of her brothers, who saw her board the bus alone. Witnesses later told investigators they saw her near Mill and High Streets in Mount Holly.

Her parents have since died, but some of her siblings are still alive. None attended the news conference.

Authorities ask that anyone with information regarding Fox’s whereabouts call the FBI’s Newark office at 973-792-3000 or Burlington City Police Department at 609-386-0262, Ext. 211.