You should break your problem into pieces, the more your understand your problems, the easiest it will be to improve:

Here 3 subproblems to begin with:

1. How to bring new visitors to your service

2. How to convert new visitors into subscriptions

3. How to retain the users

With no traffic sources, even if you convert all the incoming visitors, you will still have 0 subscriptions. It is not your case, you have the some visitors and a PR momentum so you should have enough visitors to tracks your performance on subproblems 2 and 3. Your product has a viral mechanism. That means that all your active users will expose their facebook friends (throught the vote) to your app. So you should be able to get some organic growth. (that means you shouldn't waste time on traffic acquisition)

Thus 3 success factors: - convert your new visitors into active users

- push your users to promote their "goals" to their friends

- make it easy and appealling for the friends to become user

To be sure you are working on the most important task, use google analytics and track the bottle neck. Even if most of the suggestions you've got there are good marketing tactics, if you are alone, focus on only a few tasks so you can execute them well.

Good luck !