In May 2015 (4 m. ago) I've made a simple app to send anonymous SMS to any mobile operator free of charge. The idea was to trick my friends. Nevertheless, my friends and relatives started to use this service to send each other thoughts they would never say in person. 80% of messages were romantic, 10% leaked some corporate secrets and 10% were just jokes.
Then users asked to make public Anonymous chats, similar to those, which were popular in 90's. We've done it and...Vuola! Now we have 1300+ new unique downloads and 90 000+ new anonymous messages per day. Total: 66 000 users already and 3 200 000 messages sent.
Average growth rate exceeds +300% per month.
Our team consists of 2 developers, 25 voluntary moderators and we spend 0 on marketing. Virality rules!
That's not my first social network: I started up a LinkedIn clone in Eastern Europe in 2008 and it attracted 6.5M users. In 2011 I had an exit and fell in depression. When your baby is not yours anymore, its quite frustrating.