I wouldn't consider Tumblr the most business-oriented website/blog service out there, but it's possible to generate leads form it all the same. You can send other Tumblr bloggers messages individually, just follow the instructions below. You will need a Tumblr account to complete this tutorial.

Send a message to another Tumblr author

1. When browsing the Tumble home page you'll notice avatars or profile pictures next to the blog post. Click on the profile picture.
   
2. Next, click on the envelope or mail icon in the top right of the screen.
   Note: You must be logged into a Tumblr account in order for the mail icon to appear.
   
3. Compose your email and click the 'Send' button.