How to get users for a city based micro blogging app?

I have launched an android app in India, which aims to give platform to everything happening in cities and the thoughts and ideas of people in city, just like twitter. I am having trouble getting initial users on board, what will be the best strategy to get users on board. I was thinking creating reward system for people with highest number of likes in a month and gifting them a pair of headphones or something similar, but I don't see how that can be sustainable.