And media exposure may really not help the case. Think about Lisa - she looks like a lot of babies. Having tons of tips rolling in could muddy the waters. She's also going to age fast, because babies at that age are constantly growing. If she was taken by someone who wants their own child, they probably altered her appearance and/or got out of dodge. If she wasn't taken by someone who wanted a baby, she's dead. Broadcasting her face everywhere isn't going to do much for that either.
I really can't think of the last time a public plea or airing your grief on television has actually helped recover a child. The only thing it does is follow the script of what good parents "should" do - so that they can be ripped apart by our tabloid media.
I would argue that because Elizabeth Smart's family kept her story in the public spotlight that people knew what she looked like and it led to her return.
I can think of a number of innocent parents who turned to the media to get their story out. Their child unfortunately wound up dead by a stranger or neighbor or whatever but those parents were NOT ripped apart by the tabloid media.
In the case of Lisa, I often think of where else is there to search. And then I drive to and from the airports and casinos and see areas that could be searched.......would there be people actively searching for Lisa if her parents were leading searches?
Broadcasting her face could cause the perpetrators to have guilt and maybe confess. Or at least someone close to them to turn them in.