SAN DIEGO -- The search for a missing Carlsbad hiker at Joshua Tree National Park was scaled back Tuesday, 10News reported.

MISSING HIKER Search For Missing Hiker Takes Disturbing Turn Community Holds Vigil Search For Missing Carlsbad Hiker

Eric Sears, 17, went missing Thursday afternoon while hiking with a friend at the Jumbo Rocks campground at Joshua Tree National Park in Riverside County.

Homicide detectives from the Riverside County Sheriff's Department launched an investigation into Sears' disappearance after some park visitors gave statements that led authorities to believe foul play was involved, park spokesman Joe Zarki said. According to 10News, some campers said they heard Sears and his friend arguing the night before he was reported missing.

According to 10News, no suspects have been identified.

Search crews found some of Sears' shoeprints Monday and dogs were able to pick up his scent, but the discovery led to nothing, officials said.

Richard Adler, a professional rock climber, told 10News that the search has been grueling, but he is optimistic they will find Sears.

"I'm a technical rock climber, so we were sent up to do some rock climbing to search and clear some of the upper formations to make sure Eric wasn't up there. The climb was very difficult -- it's very nasty rock -- and it wasn't pleasant, but we went up there, regardless," Adler said. "My glass is half-full. I'm going to find Eric."

The sheriff's department Sunday joined Riverside County authorities in searching for Sears, Saunders said.

Sears reportedly works at Cafe Sevilla in Carlsbad.

Separately, the San Bernardino County district attorney's office said Monday that it will file criminal charges against a 35-year-old man whose vehicle struck a van carrying five Sheriff's Department volunteers on their way to search for Sears. Two men in the van were killed.

Community Hopeful For Missing Hiker's Safe Return

Friends and neighbors held a candle-light vigil Monday night for Sears, 10News reported.

Jordan Ahle, Sears' friend and running partner, said, "I'm so grateful that people are out there to help him. We're staying hopeful and staying positive."

Ahle and others have been tying yellow ribbons on mail boxes in the Carlsbad neighborhood.

"The friends in the neighborhood have been phenomenal. A captain has been out there and some people left to search an area that has a possible lead," said, Steve Ahle, Jordan Ahle's father.

Sears' friends are not allowed to physically search because of the harsh conditions in the desert, but they are continuing the search at home. They have been passing out fliers in hopes that someone has helpful information.

Kellie Letts, another one of Sears' friends, said, "The only thing I really can do is pray and put out fliers. That's my way of helping."

Kinko's donated the 150 fliers that has Sears' picture and description.

For more information about Sears, visit www.ericsears.com.