The British teenager, from Oswaldtwistle, near Blackburn in Lancashire, has been missing in Tenerife ever since 17 June, when he vanished the morning after a rave.
The Civil Guard called for volunteers to join a “massive search” in the Masca area – near his last-known location – on Saturday and have now confirmed it has ended.
Police are keeping the investigation open and could yet open up searches in the south of the island, but have not provided an update.
A handful of volunteers turned up to help rescue teams on Saturday, forming a total group of between 30-40 people scouring a huge area of rugged and hilly terrain.
Mr Slater had been on holiday with friends on the Spanish island, when he travelled to the northwestern mountain village of Masca, after attending the NRG music festival on the Sunday night.
The following morning, the apprentice bricklayer called a friend he had been on the trip with, at around 8.30am, and said he was going to walk back to their accommodation after missing the bus – a trip that would take 11 hours.
Speaking to his friend, Mr Slater also said he was lost and in need of water, with only 1% charge on his phone.
In the days since then, local police and the civil guard, along with Mr Slater’s family, have been searching for him.
The last person to see Mr Slater was Masca resident Ofelia Medina Hernandez who spoke to the teenager at 8am on Monday 17 June.
Ms Hernandez said she told him a bus was due at 10am as he seemingly hoped to get back to his accommodation.
However, he set off walking – and she said she later drove past him as he was “walking fast”.
Since his disappearance, rumours and conspiracy theories have emerged amid online speculation on social media.
Some social media sleuths have even travelled to Tenerife to try and find him.
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