Tom Fraser, 19, from Glasgow, was seen at Inverness railway station at around 2pm on Sunday, 4 August.
He had been at the Belladrum Festival near Beauly, and his friends believed he was heading back to his home in Glasgow’s Dumbarton Road, but he has so far failed to return.
He was reported missing to the police the following day.
Police Scotland has appealed for help in tracing the teenager, who had never gone missing before.
His disappearance has been described as out of character.
Meanwhile, his mother Marina has used Facebook and Twitter to appeal for information.
She said: “Help me find my son. Thomas Fraser missing since leaving Belladrum Festival, Highlands, Scotland, 4th Aug.”
She later tweeted: “My son Thomas is still missing. Please if you have any further information let me or the police know.”
Sergeant Gerard Orr, of the West End police station in Glasgow, said: “Tom hasn’t been missing before and it is out of character for him not to contact his family and friends.
“Since Tom was reported missing, officers have been carrying out extensive inquiries in relation to his whereabouts, and have followed up a number of lines of inquiry, but we have so far been unable to trace him.
“I would urge anyone with information that may assist police inquiries, or indeed I would ask Tom himself, to contact West End Police Office on 0141 532 3350 or call 101, the non-emergency number for Police Scotland.”
The Belladrum Festival organisers also appealed for information about the teenager, asking anyone who has seen him to contact police.
He is described as white, 5ft 7in and of stocky build with light brown hair and stubble.
When last seen, he was wearing a khaki-green long parka jacket and dark jeans. Mrs Fraser has also posted photographs of her son on Facebook and Twitter.
The appeal has prompted a huge response from followers of both social networking sites.
Sarah Mackay, lead singer of Scooty and the Skyhooks, who played at Belladrum, said: “I will share to Scooty and the Skyhooks fans.”
Hugh Gruffydd said: “Pull out all the stops everyone – let’s find this young man Thomas PDQ.”
Chloe Warburton added: “I’ll retweet over the border in Cumbria. Know that I am praying for you and for your son. God bless.”
Antoinette Victory said: “Please pray for Thomas Fraser who is missing. His mother and family extremely worried.”
The teenager had been with friends at the tenth Bella-drum Festival on the outskirts of Beauly near Inverness.
Thousands of music fans flocked to the festival, which is renowned for being family friendly.