Fifteen-year-old John Wattie went missing after he left his home on his mountain bike at about 7pm on Friday.

His mother Judy Allen took to Facebook to put the word out about her missing son.

Her post urging people to look out for John, who has a medical condition which requires medication, was shared 1300 times.

John was spotted on Sunday morning by an unnamed good Samaritan who was out cycling.

The woman rode with him to his White Hills home and made sure he was returned safely to his mother.

Ms Allen said it had been an overwhelming experience.

"It was a very emotional feeling to have him home," she said. 

John is none the worse for his adventure, she said.

UPDATE: Missing teenager John Wattie has been found.

The 15-year-old was spotted by a woman who recognised him from social media posts at about 10am and was taken home. 

EARLIER: POLICE are seeking public assistance to help find a missing White Hills teenager. 

John Wattie, 15, was last seen at about 7pm Friday at his home on Plumridge Street, before he left on his mountain bike.

Police and family are concerned for John’s welfare due to a medical condition that requires medication. 

John is described as being Caucasian in appearance, 160 centimetres tall, thin build, with short brown hair. 

He was last seen wearing a green jumper, blue jeans, grey Fila shoes and a watch with a black band and fluro orange face.