Officers from South Wales Police are among those searching for a teenage girl from Bristol who disappeared eight days ago.
Rebecca Watts, 16, known as Becky, was last seen at her house in Crown Hill in St George, Bristol, on the morning of February 19th.
She left home with her phone, laptop and tablet computer but did not tell friends or family where she was going, or take extra clothing.
Avon and Somerset Police have been searching for the teenager since she was reported missing by her family at 4pm on February 20th.
Detective Inspector Richard Ocone, who is leading the investigation, said Becky disappeared between 11am and 12pm.
"From our perspective this is completely out of character," he said.
"She has not taken anything that would suggest she was going to stay away for a long period of time."
Officers are combing woodland and open spaces near Becky's home, along with house-to-house inquiries, and have searched her neighbour's gardens and outhouses.
Searches at a nature reserve, Troopers Hill in Bristol, have now concluded without anything of significance found.
Mr Ocone confirmed the search was currently remaining in the "Bristol and Greater Bristol area".
Hundreds of leaflets have been printed and a social media campaign, using the hashtag #FindBecky, has been launched by the force.
Mr Ocone said the social media campaign had been far-reaching, with almost 400,000 viewing tweets and 22,000 engaging with them by retweeting, favouriting or clicking on them.
More than two million people around the world have seen the campaign on Facebook, with 30,959 shares including in Goa, New Zealand and America.
Facebook Ads have been used to target people in the Bristol area, reaching more than 21,000 and directing hundreds to the #FindBecky page on the force website.
Mr Ocone added: "We hope that this large online presence will lead to someone remembering something from the area or days following Becky's disappearance.
"We know that Becky is very keen on social media, as are most girls her age, and so we want our online communities to help us keep our appeal for information running."
Becky is described as 5ft 4in and slim, with long, bright red hair and was wearing a dark navy blue Puffa jacket with fabric sleeves.
Anyone with information is asked to contact Avon and Somerset Police on 101, or Crimestoppers on 0800 555 111.