If you are looking for Inorganic options: best is to create Facebook & Google Advertisements
If you are looking for Organic you may try out following:
(1) Promote in Facebook groups (greater than 1,00,000 followers) of selected groups
(2) perform SEO so that your blog comes up in the top results
(3) Take help of other bloggers who have a huge following to promote your blog
(4) Try utilising local newspapers to print about your blog
(5) Have some referral scheme so that the existing users will bring in more users
Hope this helps.