By Andrea Lucia

FORT WORTH (CBSDFW.COM) – Highway signs flashing an Amber Alert for 11-year-old Jessica Smith are now showing blank screens.

Fort Worth police, though, say the search for the missing girl is still active and has now expanded nationwide.

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Warrants have also been issued against her mother, Kimberly Smith, for aggravated assault and endangering a child.

Investigators believe Smith kidnapped her daughter from their home in north Fort Worth, after assaulting her Monday night.  Investigators add Smith may suffer from a mental illness and has threatened to commit suicide and hurt her children.

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Tarrant County Sheriff Dee Anderson said the Amber Alert system is designed to spread information quickly, but not for more than a day or two.

Law enforcement are concerned overusing the alert – or constantly broadcasting one – will diminish its effectiveness and desensitize the public to it.

Police today did cancel an Amber Alert in New Mexico, where there was a reported sighting of Jessica and her mother.  Investigators reportedly found no updated information to back up that report.

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