Totally possible she's at someone's house. The reason why I first thought of abandoned buildings or homes is the vast number of them in the area, and how easy it would be to gain access to these areas. Plus, I figure there would be much more privacy to hold someone in an abandoned building than there would be a typical neighborhood house where you'd have to worry about people coming over, room mates, or nosy neighbors. Totally possible though. If she's being held, especially by gang//drug dealer types, I think the chances are that at least a few people know about it, and the more people that know what is going on the chances are better that someone will talk. Even better if it's someone Sierra knows or someone her friends know, LE should be able to make a connection. I sure hope this is the case.