Police on Hawaii’s Kauai are searching for a University of Nebraska-Lincoln student who flew to the island alone for a two-week hiking and camping trip, the Omaha World-Herald reports. Officials say they will stop their aerial searches, but will continue to look on the ground for Samuel Martinez, who arrived in Kauai on May 12. Martinez’s parents say they last heard from him just a few hours after he landed on the island. He was reported missing on May 27 after he did not arrive home in Nebraska. Law-enforcement officials say his cellphone was last active on the night of May 12; state parks and investigators have conducted searches in multiple areas nearby.

“Unfortunately, we haven’t found any sign of Mr. Martinez throughout our searches,” reads a statement from the Kauai Police Department. “We also haven’t encountered anyone who has accurately identified him and his whereabouts. At this point, there are several possibilities that could have taken place, especially on an island with dangerous terrain in places like Waimea Canyon and Koke‘e State Park trails, but we are still hoping for the best.”