A 19-year-old hiker who along with a friend has been missing in Cleveland National Forest for three days was found alive late Wednesday, Orange County Sheriff's Lt. Jason Park said.

Rescue crews ratcheted up their search of the rugged terrain about 7:50 p.m. after receiving a tip from a hiker who said he had spotted Nicholas Cendoya. The whereabouts of Cendoya's hiking companion Kyndall Jack, 18, were not immediately known, Park said.

As the search continued for Jack, Cendoya was airlifted from the canyon and taken to a hospital where he was listed in serious condition. Hospital officials told NBC4 Cendoya was foraging for food to survive.

"He is weak, severely dehydrated and slightly confused," OC Fire Authority’s Kris Concepcion said.

Waiting at the Trabuco Canyon Fire Station, a command post during the search, Cendoya's friends and family erupted in cheers when they were told the teen had been found alive.

The young hikers, both from Costa Mesa and pictured below, had called 911 at 8:30 p.m. Easter Sunday to say they were lost, but their cell phone batteries died and authorities could not locate them.

Since Monday, searchers on foot, dogs and helicopters have been combing over a network of trails in the Holy Jim Canyon area, trying to find the two teens.

On Wednesday, dozens of volunteers joined official search crews that began work at 6 a.m. -- so many extra searchers that some were turned away.

A couple of volunteer searchers had gotten lost in afternoon and were in cell phone communication with authorities, who had not been able to track them down as of 6 p.m., according to authorities on scene.

And in a separate incident in a nearby canyon, a hiker unrelated to the search was also being airlifted out -- as shown below at right -- of the area after one had injured his back after slipping and falling near a waterfall.

Russ Jack, Kyndall Jack's father, begged volunteers to stay away from the search area unless they're experience hikers. He called the scene a "modern-day circus," but assured volunteers he was grateful for their efforts.

"We don't need lookey-loos up here just hanging out and not helping. If you're not an experienced hiker or a mountain biker, then please stay home," Russ Jack said. "There's just too many people and it's hurting the efforts that the authroties have put into this right now."

Dawn Jack, Kyndall's mom, teared up in front of news cameras when the pair spoke.

"We just need our children to come home safely," Dawn Jack said. "We need for everybody else to leave here safe, so please help us out now by not coming up just to hang out … we know you love us and are supporting us."

Officials with the Orange County Sheriff's Department said enough personnel had been scheduled to continue the search through the weekend.

"We're going to increase the number of our ground searches. We're going to commence with air operations in strategic areas with high terrain that's difficult to traverse," said Orange County Fire Authority spokesman Capt. Jon Muir. "It's going to be a combined effort, and we're not going to stop until we have a good resolution."

Authorities have said the fairly mild conditions in the area are survivable, even when temperatures drop overnight. But the terrain off-trail can be difficult, and it's possible one or both of the hikers were injured, search officials said.

Russ Jack, father to 18-year-old Kyndall, has spent two nights near the search area and was clearly emotional Wednesday. He said he thought he had seen sparks of light on the hillside, but the searchers found nothing.

"After three days, you gotta say no water. The kids are dehydrated. Hopefully none of them are hurt," Russ Jack said. "At this point, everybody is still upbeat, optimistic about finding the kids in good shape and alive."

Megan Shounia, a clerk in the Trabuco Canyon general store that on Sunday sold the pair a National Forest Adventure Pass needed for parking at the trailhead, said she warned them about conditions.

"They were excited about going out. I told them to take it slow because the road is a little rocky," Shounia said. "I remember looking at their car -- it was like a green BMW. I told them to take it slow. He said he was worried about scraping up his car a little bit."

She said Cendoya wore tank top and Jack, a V-neck T-shirt.

"From what was on them, they just had the clothes on their back and a small water bottle," Shounia said.

The OC Hiking Club, which has some 2,700 fans on its Facebook page, called for "strong hikers" among its members to join in a noontime search in the Trabuco Canyon area Wednesday.

Updates were being posted Wednesday on another Facebook event page that had organized friends to search for the hikers the previous day.

Overnight Tuesday, Cendoya's car was towed under the family's direction.

A message had been drawn into the dust on the car's rear window, reading "Kyndall – we r looking, won't stop. Love you, mom."

Grief counselors were at Costa Mesa High School -- the pair's alma mater -- for the first time on Wednesday. Cendoya played football, while Jack was known as "the jackhammer" on the volleyball team.

On Tuesday, the Sheriff's Department had cautioned the many volunteers -- family, friends and others who wanted to help -- to be prepared for the search with extra food, water, clothing and navigation tools.

Authorities had said fresh spring growth was making it difficult to search off-trail through dense brush -- and to spot people from helicopters searching overhead.

"If you get off trail, you will quickly be between waist- and head-high brush...It's very difficult travel. It's hard and it's exhausting," sheriff's reserve Lt. Chuck Williams said Tuesday.

NBC4's Vikki Vargas contributed to this report.