1. I searched for journalists who have written about topics my startup was related to and shared my story and gave them sneak peek into beta version. That gave me some great visibility via blogs like thenextweb and mashable.

2. I made sure that I use write set of words and language to provoke few early users to share my beta website with their network - It was all about wordings.

3. The tweets and facebook messages that went out had similarly provoking wordings that made posts viral.

4. I launched beta version with very basic feature but started rolling out new things every 48-72 hours.

5. I used a real bad logo initially, people made fun of that logo on twitter - i used that as an opportunity to ask for help from twitter world - got 19 logo designs (some from designers at big ad agency, TV network) in my inbox in 24 hours or so.

6. I was super super quick in support - people were wow'ed by the speed at which me and my small team replied to support mails.

1 month later, we were @ 100K users and got acquired in 4th month of launch.

Hope this helps.