Here's a comment I made on The Book Marketing Network when someone asked a question about virtual blog tours.
A virtual blog tour is essentially a set of blog interviews or reviews. To set one up, you contact blogs related to your book as well as book blogs that review books and/or interview authors. Ask them if they'd like a review copy of your book and/or would like to interview your book. Tell them why your book or author would interest their audience.
Many blog interviews are done via email where you answer a set of questions and email them back to the blog owner who posts the interview on his or her blog.
By giving this procedure a fancy name, it seems more complicated than it really is. Now, some blog tours feature the same interview on more than one blog, and that is certainly a great thing because it means less work for you. There are a number of blogs that are happy to feature duplicate content since their visitors don't overlap a lot.
Of course, for a blog tour to work, you really need to locate blogs that are actually read. To locate blogs, use Google blog search or Technorati search.