A teenager missing for six days may have tried to walk 280 miles to see his girlfriend, his mother has said.
Owen Harding, 16, was last seen leaving his home in Saltdean, Sussex, last Thursday.
His mum Stella said he had been upset at being unable to get a train to visit girlfriend Meg in Pocklington, near York, amid the coronavirus lockdown.
She said relatives were desperately worried and urged the public to be on the lookout for Owen.
In an earlier appeal over her son's disappearance - shared by family friend Nadia Sawalha - Ms Harding said he had left home to watch the sunset.
Some of Owen's friends have since said they believe he has attempted to walk from Saltdean to the North, Ms Harding said.
"While it is extremely out of character for Owen to leave and not be in contact, Covid-19 has put everyone under lots of strain and we don't want to rule anything out," she said.
"Because search activity and resources are limited right now, I'm begging the UK public to look out for him whilst out on their daily walks.
"But please make sure that, in doing so, you adhere to social distancing and government guidance and do not put yourself or anyone else at risk."
Sussex Police said searches have taken place in the Saltdean and Telscombe cliffs area near Brighton.
Det Ch Insp Alasdair Henry asked anyone who was driving near the cliffs last Thursday after 18:00 GMT to check if they had dashcam footage of Owen.
He said police were keen to hear from anyone who could help, but echoed Ms Harding's request to abide by government guidance at all times.
The force would link up with colleagues across the country if there was anything to suggest Owen had travelled out of Sussex, he added.
Owen is described as white, between 5ft 11ins and 6ft, and of athletic build with short brown hair.
The appeal to find Owen has been shared by TV presenter and family friend Nadia Sawalha.
PLEASE PLEASE help FIND my daughters friend OWEN HARDING .. he is only SIXTEEN . His MOTHER is beside herself with worry . He is at HIGH RISK .You can only imagine how hard this is for his friends and family ! IF you’ve seen or heard ANYTHING please contact below ! URGENT . 🙏🙏 https://t.co/eJfHKZbjPi— nadia sawalha (@nadiasawalha) March 28, 2020