Thought I’d share this in case y’all were wondering…I just learned how to do this…

To report a user, go to Tumblr’s ‘Block’ page and enter the username you want to report, if you haven’t already blocked the account. The user will show up in your block list along with the text ‘Report for: spam, harassment.’ The words ‘spam’ and “harassment” are clickable; click the appropriate option to report the user.

(Source: ehow.com)