Forget The McCanns for a minute. What about just plain Trolling, attacking anyone who is in distress?
Something needs to be done.
The problem is, Eleanor, that there are several definitions of trolling. Some of them don't include 'attacking anyone who is in distress'. That's just your definition. Before anything can be done a firm definition has to be arrived at, one which everyone agrees on. Trolling isn't illegal and the police have said, I think, that the existing laws are fine to deal with people who break the law on the internet.
Here's a couple of definitions for you;
Urban Dictionary’s top rated definition for “trolling,” it can be defined as:
“Being a p***k on the internet because you can. Typically unleashing one or more cynical or sarcastic remarks on an innocent by-stander, because it's the internet and, hey, you can.”
Wikipedia defines it as:
"Someone who posts inflammatory, extraneous, or off-topic messages in an online community, such as a forum, chat room, or blog, with the primary intent of provoking readers into an emotional response or of otherwise disrupting normal on-topic discussion.”