When students at Nazareth Area High School in Northampton County headed back to class Monday, one familiar face was noticeably absent.

Math teacher Matthew Green disappeared on a hiking trip in California nearly a month ago, and the search for him continues.

One administrator said during a teachers' meeting last week there wasn't a dry eye in the room.

On the first day of classes, many held out hope Greene is still alive and will be found.

"They explained the situation with him being gone," said student Soren Streckman.

An announcement made Monday included a tearful message from Greene's good friends and co-workers, Streckman said.

"Their experiences and stuff, then observed a moment of silence to think about it," Streckman said.

Greene is a popular teacher who loved adventure but went missing while hiking in the mountains of California earlier this summer.

"Had a message this morning when we walked in if we needed someone to talk to, guidance counselors are here," said student Dimitri Patsis, a senior who was set to have Greene as teacher next semester. "I really hope he is out there exploring and nothing bad happened."

Friends are family are using social media to help. The "Find Matthew Greene" Facebook page has almost 11,000 likes and has raised almost $8,000 to help fund the search.

An interactive map traces spots where he was or may have been. School resource Ofc. Kim Arthur said several teachers have flown out west to search for Matthew.

"Everyone has hope and is praying for his return. Hopefully he is and maybe doesn't know who he was or maybe hurt himself and is wondering around," Arthur said.

The school district said a day-to-day, not a long-term substitute, is taking over Greene's duties with the hope of his eventual return.

"I believe having children back today is one of the best medicines in this kind of situation," said Dennis Riker, the district's superintendent.

Greene's family and friends continue to look for him in California.