The families of teenagers missing after a fire at a bar in a Swiss ski resort are facing an agonising wait for news and appealing for information about their loved ones online.

The fire in Crans-Montana was likely caused by sparklers placed on bottles of champagne that came too close to the ceiling, Swiss officials said on Friday.

An investigation into the fire will focus on the materials used at the site, the bar's fire safety measures, its capacity and the number of people inside at the time, Valais Attorney General Beatrice Pilloud said.

Swiss authorities have said it could take days if not weeks to identify the victims of the fire, which killed 40 people and injured another 119. Officials said 113 of the injured had been identified, with authorities still working to identify the other six.

In the meantime, families and friends have been taking to social media to appeal for information about their loved ones who were at the bar that night.

Among the missing is thought to be 15-year-old Charlotte Niddam, a former student at schools in the UK. The Jewish Free School in north-west London called for love and prayers, saying Charlotte had been a student there for two years before her family moved back to France.

She is loved by so many within JFS and is friends with many in our community, it added.

A statement from Immanuel College, a private Jewish school in Hertfordshire, said her family had asked that everyone keep them in their thoughts and prayers during this extremely difficult time.

Crans-Montana's tourism website lists her as a babysitter in the resort during school holidays.

The whereabouts of 16-year-old Arthur Brodard are currently unknown, his mother Laetitia said. I must find my son... it's been 30 hours since he disappeared, she told the BBC, adding that she wanted his photo to be everywhere. Some of his friends had been found with serious injuries.

Another missing teen is 16-year-old Achille Osvaldo Giovanni Barosi, who is unaccounted for after entering the bar around 01:30 local time on New Year's Day to retrieve his jacket and phone.

Italian authorities have reported six citizens remain missing, among them is Emanuele Galeppini, a junior golfer. His father mentioned that Emanuele was last heard from around midnight on New Year's Eve.

The families continue to hold onto hope, despite the dire situation, as authorities work to find answers and identify the missing teenagers.