Amber Peat was last seen at her home in Bosworth Street in Mansfield at about 17:30 BST on Saturday.
Her father Danny Peat said hundreds of people had helped search for his daughter since she left home without any money or a mobile phone.
Officers believe the teenager, who is about 4ft (1.21m) tall, is still in the Mansfield area.
Despite media appeals and a huge social media campaign, there has been no sign of her.
Mr Peat said her disappearance was completely out of character.
"She's a real home girl. She doesn't go out - all she wants to do is read a book. She would read 24 hours a day if you let her," he said.
"It's got to the stage now... we are just petrified."
Amber is white with long, dark brown hair and of petite build.
She has brown eyes and a small scar above her lip, and was wearing a black Puma zip-up top, purple trainers and blue jeans.
Mr Peat said: "She wouldn't be able to stay out. She's a tiny little thing and the weather's been freezing.
"We think she's may be in somewhere with somebody."
He said she had never been missing from home for this long.
"We just want her to know that she's not in any trouble... we just need to know that she's all right," he said.
"She's our little girl and we just want her home."
Homemade posters appealing for information have gone up in dozens of shops and houses in the area.
Yolanda Cassidy, who works in a newsagents, said: "I've heard she is a quiet girl and not really street wise, and for her to go so long without being in contact, without a phone, is clearly worrying.
"People want to help, posters have gone up all over the place. People want to see her safe."
Nottinghamshire Police missing persons co-ordinator Kirsty Gittings, said: "Amber, if you are reading this appeal please get in touch with us or your parents. They are very worried about you."
Anyone with information about her whereabouts is asked to contact Nottinghamshire Police.
Police say they are concerned for the safety of a 13-year-old girl missing from her Nottinghamshire home.