In the past, book tours typically involved planning a series of in-person events and appearances for an author to kick-off the launch of a book. This practice has evolved and is no longer approached as "one size fits all", per Mark Glesne, Senior Marketing Director at HarperCollins Christian Publishing.
Authors have a lot of freedom now in what can be done to launch a book because readers are discovering authors differently these days. Some of the components that can still be essential to a book tour are in-person signings and media appearances, but authors are expanding tours to include podcasts, bloggers, social media, and more. They don't necessarily have to go "on the road" to launch a book successfully. Glesne recommends thinking about where you and your book will flourish most, and what the best route is for bringing value to your target audience.