A new search was underway Wednesday off the Aruban coast for missing U.S. teenager Natalee Holloway, authorities said — while continuing to rebuff questions about a 19-year-old arrested over the weekend in connection with the year-old case.

The public prosecutor's office said the Aruban coast guard was using sonar and other equipment to search an undisclosed area off the Caribbean island. The search, the latest of many for the missing Alabama teen, was in its fourth day but had not previously been disclosed.

Officials also said they were also interviewing witnesses and were in contact with authorities in the Netherlands about tips received after the airing of a television program devoted to unsolved crimes.

Authorities declined to provide details about the developments or to answer questions about a 19-year-old who is being held on suspicion of involvement in Holloway's disappearance. A judge on Thursday approved a prosecution request to hold the man pending further investigation. He was also detained on suspicion of drug offenses.

Under the law, another hearing for the 19-year-old — identified only by his initials, G.V.C. — must be held by at least April 25 if the prosecution wants to continue holding him, said Mariaine Croes, a spokeswoman for the public prosecutor's office.

The 19-year-old's defense attorney, Eline Lotter Homan, declined to comment on the case.

Holloway, who was 18 when she disappeared, was last seen leaving a bar with a Dutch teen, Joran van der Sloot, and two Surinamese brothers on May 30.

Van der Sloot and the brothers, Deepak and Satish Kalpoe, were jailed and later released after a judge ruled there was not enough evidence to hold them.

Searches involving Dutch marines, the FBI and hundreds of volunteers have been conducted throughout the island and off the coast. More recent searches have focused on dunes along the island's north shore.