Robyn Gardner, 35, of Maryland, was last seen August 2 near Baby Beach on the western tip of the island, said Ann Angela, spokeswoman for the prosecutor's office. The resort town is the same area where Natalee Holloway disappeared in 2005.
Authorities in Aruba are holding a suspect in connection with the disappearance of an American woman there, the prosecutor's office said Tuesday.
The prosecutor's office released a statement later Tuesday that provided more detail. GVG told authorities that he had been snorkeling with Gardner behind Nanki Country Club when he signaled to her to swim back, the statement read. When the man reached the beach, the woman was nowhere to be found, he allegedly told them.
"The statements made by the traveling companion led to such questions that on Friday, August 5, 2011 it was decided to detain him for further questioning on the possible drowning of the woman," the prosecutor's office said in the statement, adding that police are investigating the case.
Media reports, including one from CNN affiliate WJLA in Washington, have identified Gardner's companion on her trip as Gary Giordano.
The suspect's attorney, Michael Lopez, said his client came to Aruba on vacation with a female friend he had met on a dating site and has known for years.
Lopez told reporters that his client has been cooperating with police. Lopez said that on his client's last scheduled day in Aruba, he asked authorities if he needed to stay.
"They didn't answer it, and on his way to the airport, they detained him as a suspect for murder," Lopez said.
Angela would not say what evidence led authorities to suspect his involvement in Gardner's disappearance.
Under Aruban law, a judge sees the suspect within two days of his being detained, Angela said. A judge on Sunday decided authorities may hold the suspect another eight days, she said. "So he'll be detained up until next weekend, and then the judge will see him again and the judge will decide again if he will remain in detention or go home."
After finding no trace of Gardner, authorities stopped their active search for her on Saturday and are now searching "passively," Angela said. Police helicopters and search and rescue officials are keeping their eyes out for any clues to her disappearance, "but it's not an active search anymore," she said.
Richard Forester, also of Maryland, told CNN he and Gardner have been dating for the past seven or eight months. He said that before her trip, the two argued over "the circumstances of her travel" to Aruba. He last heard from her on August 2 in a Facebook message, in which she said they would "work it out" when she got back.
Earlier that day, Forester said, Gardner posted on her Facebook wall "this sucks," with no further explanation.
She was scheduled to return to the United States August 4, Forester said.
Forester said he does not know the suspect and finds the snorkeling story suspicious because Gardner was not a fan of snorkeling.
The Natalee Holloway Resource Center -- named after a young American woman whose disappearance in Aruba made international news -- said Forester brought their attention to the case Monday.
"Gardner is described as 5'5" and 120 pounds, with blond hair and brown eyes," the center said in a news release. "She has tattoos on her left arm (back of her shoulder to her elbow), her rib cage, and her right bicep. Friends and family members are pleading with the public to help bring her home."
CNN's Josh Levs and Martin Savidge contributed to this report.