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.

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.

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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