I was re-reading Paul Grahams seminal post for Startup Founders (I have this framed and put up on a wall right outside my office) Do things that Don’t Scale.
Initial traction is hard. Recruitingusers one by one and setting a modest 10% per week growth rate should do the trick. Starting with 100 users focus on adding 10 more. And then 10% more next week. By the end of the 52nd week you will have 14000 users and in two years? 2 million.