It's a great question, and you could probably write a doctoral thesis about it in a more general sense. There are many factors, but for me the most important are these:
1. It depends on who you know. If your social circle, and wider FOAF and professional circles, consists of people who are young, dynamic, highly-educated and articulate, then you are half way there. These are people who already campaign on other issues. These are people who belong to pressure groups. They know how to start a media campaign and how to keep it going. They've got the social skills and intellectual ability, and in many cases they have the experience and professional skills (and contacts). I suspect that Alice mixed in these circles but Sophie didn't.
2. It depends on the demographics of the area. If the area has large numbers of the sort of people I am talking about above, then you stand a better chance of attention. Edinburgh does. Carlisle doesn't.
3. It depends on how much people can empathise. Alice was out for a stroll on New Year's Day. There were thousands in Edinburgh alone doing just that, and I think Alice's disappearance will hit home particularly hard with them. I don't think we have any idea of what Sophie was doing at the time of her disappearance.
OK, so I have made some sweeping generalisations and thrown in a little bit of cynicism. As I say, there are many other factors, and other people will have their own ideas. Sophie's disappearance deserves to have the same level of attention as Alice's.
