Abigail Hernandez disappeared Oct. 9 after leaving Kennett High School. She was last seen walking home at around 3 p.m., the (Concord) New Hampshire Union Leader reported.
At a news conference Friday, officials revealed her mother in Conway had received a letter from Abigail Nov. 6. The letter was postmarked Oct. 23, said Senior Assistant Attorney General Jane Young.
Young did not reveal the contents of the letter but said investigators were working to "to verify its authenticity."
"It is the one of the most tangible leads we had in the investigation," she said.
Investigators said the missing girl was not wearing winter clothing and had no money when she disappeared.
Police did not make public the contents of the teen's letter.
"We are concerned for her safety. She is not out there alone," said Young.
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