After initial traction, how do you build an exponential growth curve?

Firstly, congrats on starting to generate the buzz...

I think your main initial focus should be on customer support and product improvement till you can improve the metrics of the product. What metrics matter? Dave McClure's presentation on Startup Metrics should work well for you: http://500hats.typepad.com/500blogs/2007/09/startup-metrics.html

As you make progress with that try focusing on different marketing strategies. You eventually need to have a presence not just on twitter, but also to try to become a destination blog and by guest posting on other blogs. Ideally doing this establish yourself as a thought leader and will not only drive better ideas to you to refine your product but will also get users to hear about your product.

As you get some of the more basic marketing moving, try considering partnering with related companies/products (like twitterhawk).

Best of luck!

Congrats on getting traction!

Dave McClure's Startup Metrics is awesome, though overnight success usually takes many years of hardwork.

The resources I would like to add are the following -

• Crossing the Chasm - Geoffrey Moore - This book is said to be the marketing bible at Microsoft back in the in 90s (and probably still is). One of the key insight in this book and series is that once a software starts achieving traction, you'll need to find pockets of community users that fit the use of Tweetminer. You'll need solve all the potential adoption issues (ie signup).

Are you able to find out more from the free users on the features that they would be willing to pay for? Is there another way to monetize their traffic like the way Mint did? Or perhaps have the free users helping promote the usage of Tweetminer?

• The Tipping Point - Malcolm Gladwell - The book discusses how epidemics are spread - and in hindsight of viral adoptions of Hotmail and Skype - a great read and if you can identify amongst your users who are the mavens - and then proceed to look for more of them in the market.

• Clickbank - I see that you have an affiliate page, Clickbank traffic may be appropriate for your service.

Another thing to note, there is no link to pricing information on your site currently - while I am guessing that you are looking to convert folks to use it after they have signed up - the disadvantage is that companies that would be keen to resell this service, or recommend it to their clients, may have difficulty finding out what the cost is.

Your service seems prime for media agencies and and their clients to use.

In summary, both Crossing the Chasm and Tipping Point talks a lot about community adoption, which in momentum drives up the usage - an interesting observation of this growth is stackoverflow.com - which when they first started out, focused on software developers. Stackoverflow recently moved into high gear with penetration into different segments of their own, such as superuser.com and serverfault.com. In fact, this site is an extension of their model where the software is now used by communities for startups, parents, gamers and a lot more.

The key in the first step is to saturate a niche fully well - and thus in your case is to look at your most active users - and look to identify who and where else can you find more clients like them.

All the best!

Indeed, congratulation you for your success!

I'd personally recommend to improve your homepage, first. After all, your target audience consists of Twitter users and good stuff is viral by nature on Twitter. It should grow fast if everything's right. If it isn't, there are probably problems elsewhere. I suspect the homepage. Some suggestions:

Positioning:

• You emphasize "content discovery". This is basically an appeal to altruistic motives. Maybe, an appeal to egoistic motives would be more successful? For example, "Twitter management for professionals" would be a teaser appealing to pride.

Sales pitch:

• Same as above. Many Twitter users want more followers and spend less time. Appeal to it.
• By saying "Be the signal, not the noise" you (sort of) imply that a reader may be the noise right now. Noone really wants to be accused of that.

Social proof:

• While you have some testimonials on your site, the execution is bad. Your readers are in interesting in what they say, not who said it. Start with the quote, and end with the reference. Cut the quote if it's too long. Try to find some other sources as GetSatisfaction.
• Some positive reviews from journals would be nice.

Objections:

• If I understood correctly, the app is basically a feed reader merged with a Twitter client. People usually don't want to give up apps they got used to. So, what about import or export of OPML files, for example? What about integration with their browser or another Twitter client?

Design:

• It looks crude and unsophisticated. Readers may use it as a signal that your app is crude and unsophisticated, too. Perception influences expectations which influences judgements.
• There are some loose ends. Your landing page for the desktop client is really sparse.

Requirements:

• I got a note telling me to update on Firefox 3.5. I dunno why but stuff like that affects the diffusion of your app, of course. Additionally, it appears everytime I open a new page.

So, overall, it hard to see the benefit of the app and there're not enought signals of credibility, sometimes even the opposite. I believe if you fix that, more visitors will sign up and they will also feel more comfortable to recommend your app. Then, you'll also get the exponential growth.

Hope this helps.