Back in Dec 2012, when we were planning to launch TripTern we were bootstrapped and didn't have any money for marketing. So we relied heavily on Facebook for promotion. One thing that we used to spread the word was to create promotional material based on movie posters ( see the links below). It helped us in getting the initial signups and also was instrumental in us getting featured on Mashable.
https://www.facebook.com/useTripTern/photos/a.38683168472634...
https://www.facebook.com/useTripTern/photos/a.38683168472634...
https://www.facebook.com/useTripTern/photos/a.38683168472634...
You can see the entire album here
https://www.facebook.com/media/set/?set=a.386831684726346.90...