How to Gain a Following on Tumblr
For starters, start following others. You find others by searching their email, URL, or username. Alternatively, search for topics and blogs that interest you. You can focus on publishing-related sites, but follow sites that simply interest and inspire you too. Some people might follow you back, some might not, but it’s a start within the community.
Tumblr's sort of a blog, and sort of a social media network. If you're writing a book, start building your following NOW.