(CNN) -

Israeli police have stepped up their search for a New Jersey man who went missing while hiking in a forest outside Jerusalem.

Aaron Sofer was reported missing on Friday by a friend who he was hiking with in the Jerusalem Forest, Israeli Police spokesman Micky Rosenfeld told CNN.

Sofer, 23, from Lakewood, New Jersey, is a Yeshiva student studying in Israel.

"We are looking in a number of directions," Rosenfeld said. "It is not clear if the disappearance was personal [or a] kidnapping. It's not clear at all."

Police are searching the forest and have questioned a friend of Sofer's who was "the last man who saw him face-to-face, eye-to-eye," Rosenfeld said.

The friend "lost contact" with Sofer while walking with him and reported the disappearance to the police, Rosenfeld said.

Sofer's parents arrived in Israel on Monday.

His brother, Joel Sofer, told CNN on Tuesday that family members are "just praying hard and doing everything we could do."

He said he had visited the area where his brother went missing.

"I actually was over there today on site," he told CNN's Jake Tapper. "And you know, there's nothing. They have no evidence. They can't find anything."

Binyomin Isseeman, Sofer's rabbi in Lakewood, called the missing man a "very normal, a very healthy boy."

"His mind is clear, no problems at all," Isseeman said to CNN affiliate WCBS reported.

Republican Rep. Chris Smith of New Jersey said the U.S. Department of State was helping Israeli authorities in the search for Sofer.

"There are concerns, as we all know, about the possibility of abduction," Smith said, according to CNN affiliate News 12 New Jersey.

Sofer's disappearance comes two months after what Israeli authorities have called the revenge killing of Palestinian teen Mohammed Abu Khedair, 16. His body was found in the Jerusalem Forest on July 2, just miles from where Sofer went missing.

Two minors and an adult were indicted in the killing. Prosecutors allege the killing was retaliation for the deaths of three Israeli teens whose bodies were found in the West Bank in June. One of the Israeli youths also had American citizenship.