Want the best of The Telegraph direct to your email and WhatsApp? Sign up to our free twice-daily Front Page newsletter and new audio briefings. A search has been launched for a 13-year-old girl who left the country via the Channel tunnel. Police believe she was accompanied by an unknown adult.Serena Alexander-Benson was last seen by her father leaving their home in Wimbledon just before eight o’clock on Friday morning.She was dressed in her green school uniform, and told her father she was going to school. But she did not arrive for class and has not been seen since.Serena lives with her father in Wimbledon. Her mother lives in Poland. She has never been missing before and police are concerned for her welfare.Detectives from Wandsworth CID have established she left the UK via Folkestone in the morning of Friday May 25, on a EuroTunnel train.In a statement, Scotland Yard said she was “probably in the company of an older person” but the Telegraph understands detectives have not yet ascertained whether the young girl is in the company of a family member.Police said an active investigation was underway and anyone with information about her whereabouts, or who may have seen her as she travelled through Folkestone, should call Wandsworth CID on 0203 276 2588.