Robert Thomson hasn’t been seen by family and friends since his dad left him at a bus stop in Bellshill on Friday.
He missed his 18th birthday which was yesterday (Wednesday).
Mum Hazel Doonan, of Community Road, Bellshill, said: “I sat up till 2am, hoping he would come home for his birthday. I had a cake ready and banners in the windows.
“It’s a nightmare. I just want a phone call to say he is definitely all right.”
Hazel said as far as she knows Robert had no money with him and no change of clothes. Calls to his mobile phone are going directly to voicemail.
She added: “I don’t understand it as his phone is never out of his hand.”
Hazel said Robert was in good spirits and looking forward to his birthday when he left the house early on Friday evening last week.
He was with his dad, Alan, who left him at a bus stop in Motherwell Road. Robert said he was going to see a pal in Motherwell’s Jerviston area.
Hazel insisted Robert’s disappearance is out of character. She thanked friends who have helped search for him in areas including Motherwell, Strathclyde Park and Viewpark in recent days.
She said her son was wearing a black Lacoste tracksuit top, dark trousers, black Nike trainers and a baseball cap when he was last seen.
Robert has four brothers and two sisters.