Jay Slater: Missing man in Tenerife was on first holiday with friends
Shortly before 09:00 BST that morning he called his friend Lucy and said he was trying to make the 10-hour walk back to their accommodation in Playa de las Americas, but needed water and had 1% battery on his phone.
The call then cut out and Mr Slater has not been seen or heard from since.
Social media posts from Sunday evening showed a smiling Mr Slater in a grey t-shirt with green patches on the shoulders.
He also posted an image at 07:30 showing his hand holding a cigarette at the property he travelled to with the two men.
His last known location was on a path in the mountainous Rural de Teno national park in the north-west of the island.
Ms Duncan told the BBC: "I've not slept at all, it's like it's not real.
"It was his first holiday abroad with his friends and I was encouraging him to go, I said 'you will have a great time'."
She said she and her son's friends had pieced together his movements on the night he was last seen, determining that he left in the car possibly at about 06:00.