(just my opinion)
i started reading this info about Natasha today so I don't know all of the details, but I was trying to figure WHY she would not make contact w/her father or grandmother, especially if she knows how to make collect calls and is able to. She could've at least borrowed a cell phone from a friend at some point. I wonder if maybe she doesn't just doesn't want to be found. What would be the reason? If she is computer saavy, at the very least she would've googled her own name before and could easily see that she is a missing person. If you are looking for websites that she could be on now, such as a myspace.com, if she is there, then she obviously doesn't want to be found.
Although I think her father deserves to know what happened to her, I think it's important to know if there was a good enough reason for Natasha to go with a mother that she may not have been close to. Was she suddenly uncomfortable around her father? It doesn't sound like things were going very well in her world. Maybe she wasn't comfortable with her grandmother.
Since no one knows what happened to her, then i think they should be focusing on her step father, the lead where she seen w/a pimp, etc. or if any foul play is involved.