KADENA AIR BASE, Okinawa — Air Force helicopters from the Okinawa-based 33rd Rescue Squadron searched for a second day Friday but were unable to find a missing American hiker on Kuchinoerabu Island, Air Force officials said.

The four helicopters, diverted from a training mission Thursday, joined Japanese search teams that had been scouring the tiny island since Monday for Craig Arnold. The 41-year-old poet and assistant professor from the University of Wyoming has been on a five-month trek to Japan’s volcanoes.

He was doing research for a lyrical book on volcanoes and kept a blog of his travels called "Volcano Pilgrim" at http://volcanopilgrim.wordpress.com.

On Tuesday morning most of the island’s 155 residents and 40 police officers searched the area, Kagoshima Prefectural Police spokesman Yoshiyuki Kuzuhara said.

The search was suspended after three days when no trace of the poet was found. However, it was resumed when a friend of Arnold’s in the States reported that Arnold had accessed his Facebook page for a minute Thursday.

Kuzuhara said Arnold has not responded to calls to his cell phone. He added that the search will extend through Sunday.

Arnold arrived on the island Monday by ferry. He checked into a guest house, leaving his luggage before heading toward Mount Shindake, a 2,170-foot active volcano, Kuzuhara said.

An island resident gave Arnold a ride to the foot of the precipitous mountain before he walked into the dense jungle alone, Kuzuhara said in a telephone interview with Stars and Stripes.

The islander told police the American carried just two walking sticks and no water or food.

The owner of the guest house reported Arnold missing after he failed to return Monday after dark.

The island, about 88 miles south of Kagoshima, is a popular tourist destination with numerous hot springs and fishing spots. But Mount Shindake is not a place where most hikers would go, especially alone, Kuzuhara said. An off-limits sign is posted at the head of a trail leading to the mountain.

"It is a very dangerous place, with the entire mountain enveloped in sulfur gas," he said.