A billboard on the Eastex Freeway is the latest effort to find a Spring girl who went missing four years ago.  Sunday is National Missing Child Day. 

Clear Channel Outdoor's Lee Vela says it's hoped somebody who knows something about Ali Lowitzer's disappearance sees the digital billboard and makes the call.

“We hope by putting this message up,” Vela says, “that somebody somewhere knows about this young lady and -- hopefully, she'll be found.”

The girl went missing April 26th, 2010.  Her mother has never given up the search.  She says Ali got off her school bus just three houses down from her home – and was never seen again.

With emotion in her voice, JoAnn Lowitzer says finding Ali is her main job.

“Every day,” she says, “I try to do something to further the investigation.”

Vela says the electronic billboard is in a high-traffic location at FM 1960 and the Eastex Freeway.

“It is one of the highest traffic areas in Houston,” he says, “so this ad will be seen by approximately 80-thousand people per day.”