Update 4pm: There’ll be further details later, I’m sure, but this young walker has been found alive and well this afternoon. A passing leisure boat, the Flipper Uno, appears to have spotted him making signals in the barranco Seco area near the Los Gigantes cliffs. A GES helicopter rescued him because access by foot was very difficult. He was flown to the Adeje heliport, and from there transferred to Hospiten Sur where he is said to be fine, and suffering only from minor injuries.
Update 20 January: The search for this young walker has resumed this morning, with GES, Bomberos and Guardia Civil again meeting in Masca, joined by a search and rescue helicopter. Last evening before it became dark ground teams had managed to get down to the coast without any sign of him.
Original post 19 January: Search and rescue teams are currently in action in Masca barranco after a 17-year-old Russian youth was reported missing by his family earlier today. Presently involved are Guardia Civil, GES, Bomberos and guardias de caza (security and protection agents for hunting areas).