There's a lot explained in the BBC article in the OP.
[quote]Reporting from the scene, the BBC's Nick Garnett described the Rural de Teno as a "remote and wild national park", with cold nights and high winds.
[quote]"Deep ravines and huge daunting mountains make the national park a difficult place for the Spanish search teams to navigate, but one mountain rescue worker told me this is not the first time they’ve been called out to the area," he said.
[quote]"At night, the countryside becomes a maze, pitch black and disorientating."
[quote]He said search and rescue teams are concentrating on one particular valley near the top of a mountain pass, and a helicopter has been sighted for the first time this afternoon.
And more:
[quote]Mr Slater's mother, Debbie Duncan, has told the BBC her son was on his first holiday abroad with friends.
[quote]She flew to the island and joined the search, and said: "I've not slept at all, it's like it's not real."
[quote]Apprentice bricklayer, Mr Slater, from Oswaldtwistle, had attended the three-day NRG music festival in Playa de las Americas in the south of the island.
[quote]He left with two men he met there and ended up in a house about 40 minutes drive away in a rural area.
[quote]Ms Law said he told her he had missed a bus, and was instead attempting the 10-hour walk back the accommodation, but the call then ended.
[quote]When the Guardia Civil spokeswoman was asked if officers had spoken to the two men Mr Slater left the festival with, she said: "It's part of the investigation, I cannot tell you more."
BBC article at R33 about the search being called off (though the investigation remains active):
[quote]The apprentice bricklayer, from Oswaldtwistle, had been attending the NRG music festival on 16 June, and his friends said they were out in the tourist hotspot of Playa de las Americas when he was seen getting into a car with two British men he met earlier in the night.
[quote]The next morning, 17 June, he was tagged in a photo posted on Snapchat at 07:30 BST at an Airbnb in Masca, which was reportedly being rented by the two men.
[quote]Investigators have spoken to the pair and they are "not in any way relevant to the case".
[quote]He was last heard from before 09:00 BST in the Rural de Teno Park, where he called a friend to say he had missed the bus and was trying to make the 10-hour walk back to their accommodation in the south of the island.
[quote]Lucy Law said Mr Slater told her during a frantic phone call that he was "lost in the mountains", desperately needed a drink and had 1% battery on his phone.
[quote]Best friend Brad Hargreaves told ITV's This Morning he received a video call from Mr Slater around the same time in which he appeared to be sliding off a designated path, with the call showing his feet on rough ground.
So it's obvious the police thinks he got lost and died of exposure.