Signs That Missing New Hampshire Teen is Alive

A letter arrives concerning Abigail Hernandez almost a month after her disappearance.
3:00 | 12/07/13

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Transcript for Signs That Missing New Hampshire Teen is Alive
new hope that a teenager missing since october may actually be alive. Abigail hernandez, the 15-year-old from new hampshire, went missing walking home from school. Then a month later, out of the blue, a sign in the form of a letter. With this letter, concern that abigail may be in grave danger. Linzie janis has more. Reporter: Police are revealing evidence in the disappearance of abigail hernandez, the 15-year-old who hasn't been seen since leaving her new hampshire high school on OCTOBER 9th. Authorities now say the teen sent her mother a letter, two weeks after she mysteriously vanished. Law enforcement had to take every possible step to verify its authenticity. We believe that it was, in fact, written by abbie. Reporter: Investigators are not disclosing the content of the letter. But are convinced abigail may be in grave danger. Someone may be now coercing her. Someone may now be manipulating her. And her safety is absolutely in question. Reporter: Police releasing photos of a necklace and purse abbie had been known to wear regularly. And appealing to the public for help. We're asking you, look at your neighbor. Look at the grocery store. Look at your church. Is there somebody that you haven't seen here before? Reporter: This is the last known photo of abbie, seen walking through the hallway of her school on the day that she vanished. Police say that evening was the last time her cell phone was used. Investigators have been searching ever since, knocking on doors, looking in the local woods and river. Abigail's distraught mother, delivering ts message to her daughter just days after she went missing. Abbie, please come home. We miss you so badly. Reporter: The fbi investigator working on the case says receiving the letter is unprecedented. He hasn't seen anything like this in recent investigations. And it gives him hope that she's still alive. Again, they're worried she may be being held against her will. It's such a remarkable development. We hope for the family's sake, they find her soon. A lot of other news breaking

This transcript has been automatically generated and may not be 100% accurate.

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