Official Leaderboards are being worked on for the Dota 2. They will be based on solo MMR and there will be some eligibility requirements based on number of lifetime games played, as well as number of solo ranked games played within a recent time period. The details are still being finalized and more info will be available when the first leaderboards are active.
Client notifications were sent to about a thousand players requesting official player data that will appear on the leaderboards. Unfortunately, many players who are eligible have not yet responded. Be the first leaderboard can be posted, more info on player profiles is required.
So if your solo MMR is high (>5000 or so) and have played several solo ranked games recently, check your client notifications. If you have a pending request for official player information, please submit it!
If you didn't receive a notification, don't worry! If, at any time in the future, you are within reach of a leaderboard and meet the eligibility requirements, it will be made possible for you to submit your information and appear on the leaderboard.
TL;DR: Leaderboards being worked on. If your solo MMR is high (eg: 5000>) check your notifications. If there is a request for player info, please submit it.