North Wales Police said they found the bodies in a vehicle which appears to have left the road in Garreg, near Tremadog.Jevon Hirst, Harvey Owen, Wilf Henderson, and Hugo Morris were last seen on Sunday morning in a silver Ford Fiesta with the registration HY14 GVO.
North Wales Police confirmed shortly after midday on Tuesday the car had been found by officers.
"Emergency services are currently at the location and the families of those involved have been kept updated," the force said earlier on X, formerly Twitter. "Further info will be released when available."
A van bearing the words 'collision forensics' was seen arriving at the scene shortly after 2pm, according to Sky.
An air ambulance is believed to have landed nearby, with the Welsh Ambulance Service confirming it had been called to the scene shortly after 10am.
It was called to reports of an incident near the A4085 between Nantmor and Tan-Lan in Gwynedd, on the edge of Snowdonia National Park, said a spokesperson.
"We sent an operations manager, two emergency ambulances and two Cymru High Acuity Response Units to the scene where we were supported by the Emergency Medical Retrieval and Transfer Service in two Wales Air Ambulance charity helicopters," they added.
A police cordon was established near the village of Garreg on the A4085, near where the car was found.
Police and rescuers have been carrying out a major search for the four boys in Snowdonia, where they are believed to have gone camping. The search has been focused on the areas of Harlech and Porthmadog. The car is understood to have been found around 7km from Porthmadog.
Earlier on Tuesday Lisa Corfield, the mother of Wilf's girlfriend, told MailOnline the boys, thought to be sixth-formers from Shrewsbury, "are not experienced campers".
Officers searching for four missing teenagers in the Porthmadog area have located the vehicle they were travelling in.
Emergency services are currently at the location and the families of those involved have been kept updated.
Further info will be released when available. pic.twitter.com/1lWQLs2O1e
— North Wales Police (@NWPolice) November 21, 2023
"They have never been there before," she said. "[They] were just going for the night so have a tent and sleeping bags but only the basics."
Meanwhile Mr Owen's mother, Crystal Owen, said she had not known they boys were planning on camping, and had thought they were going to stay at friend’s grandfather’s house.
“I am frantically worried," she told the BBC. "We haven’t slept a wink, we are desperate to chase any lead we can.
“If I’d have known [where he was going] I wouldn’t have let him due to the winter weather conditions.
“They are all sensitive, intelligent lads and we are just hoping they parked up, got lost and are OK.”
Another parent of the boys shared the police's appeal on social media, writing: “Please keep sharing… if anyone knows anything or can think of anything that may help find the boys please contact the police. We are desperate for any news.”
Harlech and Porthmadog are towns on the North Wales coast. Harlech lies within the vast, mountainous Snowdonia National Park - a hugely popular area for hiking - while Porthmadog is just outside it.
Mountain rescue teams and are said to be searching for the car they were travelling in. A helicopter is also understood to have been involved in the search.
Chris Lloyd, chairman of Ogwen Valley Mountain Rescue Team, told the BBC on Tuesday: "We were called out by North Wales Police early yesterday afternoon.
"Our first job was to look for any indication they were on the mountain.
"We deployed two or three teams to drive around all the car parks. We cannot find the car. We are still actively looking for it and are continuing to search. We don't have specific area where to search."
Anyone who sees the young men are asked to contact North Wales Police quoting A184194.