Friend and family of missing Pennsylvania teacher Matthew Greene are holding out hope that the experienced hiker will be found alive after he disappeared in California more than one month ago.

The disappearance of Greene, 39, who teaches high school match in Nazareth, Pa., and lives in Bethlehem, has left his family scratching their heads.

"It just doesn't seem to me that he would go out for a day hike and not return," Greene’s sister, Tiffany Minto, told the Associated Press. "We can't visualize him getting himself into any kind of dangerous situation. He's the personality type who would just turn back if it was too dangerous."

Greene’s disappearance led to the creation of the Find Matthew Greene Facebook page, where family and friends post updates on volunteer searchers and assist in the effort to help find the missing Pennsylvania teacher.

The page was updated Sunday night by a friend of Greene’s sister, who posted this interactive map of the mountains and terrain Greene recently climbed around Yosemite National Park. The map also shows locations where Greene was seen before his disappearance.

Greene was first reported missing July 29 to the Mammoth Lakes Police Department. He was last known to have been camping at the Shady Rest Camp Ground while his was waiting for his car to be repaired.

Greene’s brother-in-law, Ron Minto, told ABC News that it was unusual for the 29-year-old to not be in touch with his family for such a long length of time.

"We started to call up some close friends," he told ABC News. "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.'"

Minto acknowledged that the task of finding his brother-in-law will be arduous.

"This is extremely difficult terrain," he aid. "This means a hike where you come across a 20 foot wall and you have to get over that wall with nothing."

On Friday, Ron Minto posted to the Facebook page an image of eyeglasses closely resembling ones worn by Greene, but it’s unclear whether authorities determined that the glasses belong to the missing Pennsylvania math teacher.

“We are working to secure these glasses now, they were found by a hiker and being delivered to the Police as I type this. I have a few other pics of these I will try and post but we believe probability is high these are Matts ~ Ron,” Ron Minto wrote.