Search efforts for a 39-year-old missing hiker who was last heard from three weeks ago in the Mammoth Lakes area were at a standstill Wednesday due to a lack of information and questions over jurisdiction, according to the man's family.

Matthew Greene, of Bethlehem, Pa., called his parents July 16 to let them know he was waiting for a Mammoth Lakes repair shop to fix a blown head gasket on his car while his friends continued on to the next destination on their trip.

Authorities said phone records show it was the last call Greene made from his phone before either the batteries died or it lost signal.

"We are pleading for everybody to spread the word," said Greene's younger sister, Tiffany Minto, who has set up a Facebook page dedicated to raising awareness of his disappearance. "We're hoping to get his face out there so someone will recognize him and come forward. We think that will be the difference in finding him sooner rather than later."

Before he went missing, Greene arrived in Mammoth Lakes on June 27 for the start of an annual summer hiking and climbing trip he took with friends.

The avid outdoorsman apparently planned to camp at the Shady Rest Campground and reunite with the rest of his group after retrieving his car from the shop. Greene's friends reported him missing July 29 after discovering he had left his campsite at some point and never returned.

Greene's car had been finished for nearly a week and credit card records showed the last purchase he made was also on July 16, the same day of his final phone call.

It is unknown the exact day Greene left his campsite or where he was going, but Mammoth Lakes police said they believe he may have gotten a ride from someone to a remote location to hike or climb.

Friends told investigators that Greene had previously expressed interest in mounts Banner, Ritter, Lyell and the Tuolumne Meadows area.

The Mono County Sheriff's Office said it couldn't launch a full-scale search effort without more information to narrow down where crews should begin. Minto said another issue was the fact that Tuolumne, Madera and Mono counties meet at a point, throwing into question which agency should be responsible for the search.

Yosemite National Park and Tuolumne County Sheriff's Office officials said they were aware of Greene's disappearance, but neither agency had been requested to assist with the search.

A Mono County search-and-rescue team over the weekend sent ground crews to the Ritter and Banner peaks as part of a training exercise, but they didn't find any clues to Greene's whereabouts. A California Highway Patrol helicopter didn't locate Greene during a brief aerial search of the area on Sunday.

The SAR team has verified that Greene did not sign the summit registers at Ritter or Banner. The team is also currently analyzing U.S. Forest Service permits and emailing permit holders to try and find someone who may have seen him.

A Yosemite crew confirmed Greene had not signed the register at Lyell, according to the park.

"We're feeling very helpless and overwhelmed," Minto said of the past few days. "We want him back in good condition, but at this point we also would just like to know what happened. It's very frustrating not having any information that could help lead to answers."

Minto's "Find Matthew Greene" Facebook page has attracted more than 6,000 followers since last week. She hopes the story will receive attention in the national news media so it can reach anyone who may have encountered her brother but since left the area.

Greene worked as a math teacher at Nazareth High School, about 20 minutes outside of Bethlehem, where faculty and students held a candlelight vigil for him Tuesday night. Students and parents from Greene's first post-college teaching job at Twin Valley High School have also expressed support.

"The response has been overwhelming," said the missing hiker's father, Robert Greene, of Lehighton, Pa. "It's unbelievable and we're all really appreciative. Whatever the outcome may be, we would like to thank the folks who are out there doing whatever they can."

Robert Greene said some of his son's friends were en route to Mammoth Lakes to help search.

Mammoth Lakes police said Matthew Greene is 5-foot-11, about 160 pounds and believed to be wearing yellow hiking boots, a blue hat, gray-and-black backpack and a dark green or black shirt.

Anyone with more information is asked to contact Mammoth Lakes Police Department at 760-934-2011, or the Mono County Sheriff's Office at 760-932-7549, ext. 7. Minto's Facebook page can be found at