I've been feeling the same way about my startup, which has almost 17,000 users but only a small amount of them are paying customers (launched a paid plan a few months ago). I keep wanting to ask myself how much longer I should give it to see if it reaches profitability, or should I just shut it down? Anyway, right now I'm creating a survey for the paying users to be able to tell what they like/don't like about the paid plan. I also plan on doing a referral program that benefits both parties (I did get both of those ideas from a slideshow about a startup and their freemium model, forgot which). Keep those ideas in mind if you ever plan on introducing any paid plans and good luck.