Math Teacher Mysteriously Vanishes on Hiking Trip The family of a missing Pennsylvania high school math teacher is spearheading the search for the 39-year-old hiker who vanished on a trip to conquer the peaks of the Eastern Sierra in California over one month ago and has not been heard from since. Matthew Greene, 39, of Bethlehem, Pa., was reported missing on July 29, according to the Mammoth Lakes Police Department. He was camping at Shady Rest Camp Ground waiting for his car to be repaired at a local shop, but no one has heard from him since July 16. Police believe he may have gotten a ride from someone to a remote area to hike or climb. Greene, a math teacher at Nazareth Area High School in Nazareth, Pa., was an avid hiker who went on summer-long hiking trips for as long as his family could remember. This summer was no different. "As soon as school let out, he drove all the way out there [to California]," his sister, Tiffany Minto told ABCNews.com. But on his drive to Mammoth Lakes, Calif., he started having car trouble. Once he arrived in town, he brought his Subaru to a local repair shop to get it fixed. But the shop kept pushing back the timeline for repairs, Minto said, and Greene's friends ended their trip while he waited for his car to be fixed. Matt [told his friends], 'Go on without me, I'll catch up with you. My car will be ready in a week,'" Greene's brother-in-law, Ron Minto, told ABCNews.com. They went to Colorado without him, and that's when they started to get concerned. But Ron Minto said that after a week went by where no one had heard from Greene, they became alarmed. "We started to call up some close friends," he said. Once we started to gather more information, we said, 'This is strange. This is highly unlike Matt. He's a highly meticulous person. We knew something was wrong.' The last time anyone heard from Greene was on July 16. He was texting with friends before going to bed around 9:30 p.m. at Shady Rest Campground, "but from there, we don't know what happened," Ron Minto said. Since local authorities are unable to initiate a search for Greene without confirmation of his last known location, Greene's family has stepped in to helm the search. Minto said he and his wife have been crowd-sourcing support from social media platforms like Facebook, Twitter and Instagram, as well as through hiker and climber forums, to gain leads in their search for Greene. While they are working with the Mammoth Lakes Police Department, "they are limited in their resources," Ron Minto said. What makes the search even more difficult for the family is the fact that this area is not your typical hiking country that anyone can search and scale. "This is extremely difficult terrain," Ron Minto said. This means a hike where you come across a 20 foot wall and you have to get over that wall with nothing. Still, grassroots efforts have turned up possible clues. Overnight, a hiker found what appeared to be glasses similar to the ones Greene wore at one of the trailheads in the mountainous area and are working with local law enforcement to figure out if they were his. "His prescription is unusual, so it's a really good indication," Minto said of the find. Matt has a really bad astigmatism. Without glasses, he can see about as far as an arm's length. Minto said a hiker contacted him after finding the glasses on a day hike about a mile out of town. The hiker knew about the search for Greene and thought the glasses looked similar to the ones he wore. People have pooled their resources and time to help the family search. Ron Minto said that volunteers have offered the use of a helicopter and plane flyovers as well as high definition cameras. "The outpouring of prayers, love and concern that people have shown, it restores your faith in mankind," Greene's mother, Patricia Greene told ABCNews.com. Most of these people never met Matt. They don't know him, but they're giving their knowledge, expertise and time [to find him]. We're thankful for every one of them. Still, the high altitude and difficult terrain pose challenges in the search. We understand it's an extremely dangerous terrain and the risks that are involved. It's been over 30 days," Ron Minto said. There are crevasses in glaciers, where the ice is melting. They can open up and swallow you and no one would ever be seen again.  Still, they remain hopeful for his safe return. We're still holding out. Miracles do happen," Patricia Greene said. Whatever the outcome, we just want him found and brought home. Green is 5'11" and 155 pounds, with brownish-blonde short hair and blue eyes. Anyone with information about his whereabouts should contact the Mammoth Lakes Police Department or Mono County Sheriff's Office.