Alisha Watkins, 14, was last seen in Cardington, Beds, on Saturday, September 29.
In an emotional appeal on social media, mum Claire Watkins said: “I feel she’s in trouble or something’s happened.”
She added: “It’s unlike her to go this long without contact.”
Posting a picture of Alisha on Facebook, Ms Watkins also wrote: “This is a cry for help... The family are besides ourselves with worry.
“Has anyone of Alisha’s friends heard from her since Saturday afternoon; Has anybody seen her.”
Bedfordshire Police described Alisha as being around 5ft 4ins tall, slim and having blonde hair.
She was last seen wearing black leggings, a navy puffa jacket and black trainers.
Anyone with information about Alisha is encouraged to call 101 quoting reference number MPC/4087/18.