15th
You need to be popular, otherwise you will never find yourself on the list.
Too bad as most of the time it’s not the most popular ones around who are the most interesting.
Directories based only on popularity (like the new Tumblr one) are not necessary the best way to find people you may like following, It’s a vicious circle as the most populars just become more and more popular burying the others in the endless list.
Tumblr tried, with their Tumblarity ranking, not just to take into account the number of followers, but it certainly counts as the most important one. The two secondary elements in their algorithm are certainly the number of likes and reblogs of your posts. Two things that are in direct relation with the number of followers you have. More you have followers, better are your chances that your original posts will be liked and reblogs by many.
I think a directory who can promotes new users, latest post by category and subject whatever if they are popular or not may help people get in contact with each other and weaves a more diverse social network.
We are not there yet.