This question has been asked many times by many people. So, let us discuss it. Personally, I can see, some users are taking less interest in Tumblr nowadays. However, it is not dead yet as there are still over 5 million users on Tumblr worldwide, including me.
In today’s era, there are many apps and websites like Instagram, Twitter etc, that are grabbing more attention among the users. That doesn't mean Tumblr is dead or unpopular. Basically, it depends upon the choice of the people, their priorities, and of course, the purpose for which, they are going to use these social media sites.
For microblogging and posting interesting content, it will always occupy the top position among other social media websites.