ORANJESTAD, Aruba (AP) -- Ten more FBI agents headed to Aruba on Saturday to help search for an Alabama teenager whose disappearance on the last day of a high school graduation trip has shaken the quiet Dutch Caribbean island.

Police and volunteers combed beaches and scrubland for a fifth consecutive day, but found no sign of Natalee Holloway, 18, whose mother had tearfully pleaded for more U.S. help in the search.

Ten more FBI agents were joining the three already on the island, said Attorney General Caren Janssen.

"We need more technical assistance," Janssen said, declining to elaborate.

U.S. State Department spokesman Sean McCormack had said Washington was "making sure that we provide all possible assistance to the family and local authorities."

Holloway's mother and stepfather rushed to a police station late Friday night when police thought they might have found the teen in a car with some Arubans. Police said they detained a young American woman -- a blonde like Holloway -- because she presented what they suspected was false identification.

Holloway's mother and stepfather held hands and smiled as they emerged from the station outside the capital of Oranjestad, saying the woman was not their daughter but they were confident she would be found.

"I know we'll find her," Beth Holloway Twitty said.

Aruban Prime Minister Nelson Oduber said Holloway's disappearance has dismayed an island that prides itself on its safety and friendliness -- a haven for the 500,000 American visitors last year.

"Learning the news of Natalee's disappearance on our island left us all in a state of shock and disbelief," Oduber said. "We will not tolerate any activities that harm our American friends or tarnishes Aruba's reputation."

Authorities say there is no evidence the honors student and Mississippi native was abducted, but police commissioner Jan van der Straaten said "after four or five days you are afraid a crime has been committed."

Her mother had pleaded earlier Friday for the Dutch government to request more direct help from the United States.

"We all have a common goal to find Natalee so we can bring her home," Holloway Twitty told reporters in a hotel conference room. She choked up and left the room in tears.

A $50,000 reward has been offered for information leading to Holloway's rescue, said Myrna Jansen, the director of Aruba's tourism office. The Aruban government and local tourism organizations were contributing $20,000, while family and benefactors in Alabama were offering the rest, she said.

Aruba's coast guard began searching surrounding waters, indicating authorities were considering the possibility Holloway was taken off the island with or without her consent. Police found her passport in her hotel.

Police receive tips every hour, but "none has proven to be the golden tip," Janssen said.

Holloway spent the last night of her holiday at Carlos 'N Charlie's bar and restaurant in the capital, eating and dancing with classmates and residents. She didn't show up for her return flight.

Justice Minister Rudy Croes said police questioned and released two Surinamese nationals and a native of the Netherlands who said they dropped Holloway off early Monday at the Holiday Inn where she had been staying, rectifying police reports that the three men had been Aruban students. He said the three men were residents of Aruba.

The search has not been extended to Venezuela, whose coastline is only 25 miles from Aruba at the nearest point, or the neighboring Dutch island of Curacao, van der Straaten said.

Holloway earned a full scholarship to the University of Alabama, where she planned to study premed, said her uncle Paul Reynolds, who traveled from Houston to help in the search.

Island noted for friendliness
Reynolds said his niece was a responsible person who would not have run away.

"Natalee is very smart and focused," Reynolds said. "It never crossed my mind that she intentionally missed the flight. When she did, I knew something was terribly wrong."

Posters with a photograph of Holloway have been put up throughout island, with a caption reading: "Kidnapped since 1:30 a.m. May 30."

On an island remarkable for its friendliness, pristine beaches and an absence of violent crime, Holloway's disappearance has shocked islanders, many of whom say they are optimistic she will be found alive.

"She's not on the island," said Jany Winterdal, a 51-year-old taxi driver. "In Aruba, we don't know what doing bad things to people is. For me, she's alive."

There have been two murders and three rapes on the island of 72,000 people this year, compared to one murder and six rapes last year, none involving foreigners, police said.

Aruba has an average of 13,000 tourists on any given day at this time of the year, the Tourism Authority said.