Police in Tenerife have called for more volunteers to take part in a mass search to comb the expanse of rocky wilderness where Jay Slater disappeared. The 19-year-old from Lancashire was last heard from on the morning of Monday 17 June when he texted a friend to say he had no water and only 1% battery left on his phone. Slater had been on holiday with friends and had gone back to a rented house in a rural part of the island with people he had met at a festival. As the search for the apprentice bricklayer entered its 12th day, Tenerife police urged those willing to volunteer to register to take part in a planned search on Saturday of the rocky area close to where he went missing. Tenerife’s Civil Guard police chief, Angel Sanz Coronado, said: “Following the disappearance on 17 June of the young 19-year-old British man in the area of Masca, belonging to the municipality of Buenavista del Norte, the Civil Guard is prepared to carry out a mass search. “Given that it is a steep, rocky area, full of uneven terrain and with many ravines, tracks and trails, we request the collaboration of all those volunteer associations that can help in this planned search that is intended to be carried out in a directed and coordinated way. “This massive search will begin on Saturday 29 June at 09:00 hours. A meeting point will be established at the Mirador de la Cruz de Hilda in Masca to start the search in a logical and orderly way along the many paths and ravines that are found in Masca.” David Cameron, the UK foreign secretary, said he was “thinking of and worrying” about Slater and that consular assistance was being given to the family. On a campaign visit on Thursday to Rolls-Royce in Barnoldswick, Lancashire, Lord Cameron said: “Obviously I am thinking of and worrying about the family and this young man. Consular officials are there in Tenerife talking to the family, talking to the local authorities there and desperately keen that we make progress and find out what’s happened.” The Masca gorge, where the search is taking place, has already been searched by police with dogs and by helicopters and drones, which turned up no trace of Slater. He is not the first person to disappear in the area and locals said it could take months for the bodies of missing people to be found. Slater’s mother, Debbie Duncan, who has been on the island searching for her son for more than a week, said she was not losing hope that he would be found alive. A GoFundMe page set up for the search for Slater surpassed £40,000 on Friday, and Duncan said the money would be used for mountain rescue, accommodation and food expenses. In an update on the page, which was started by Slater’s friend, she wrote: “I wanted to share that these funds will be used to support the mountain rescue teams who are tirelessly searching for Jay. Additionally, since our stay in Tenerife needs to be extended, we will also use the funds to cover accommodation and food expenses. “I’m surrounded by wonderful people who are by my side but far from their loved ones, so we’ll also be using part of these funds to fly them to Tenerife so we can support each other during these dark times.”