Check Out Twitter's Growth Versus Facebook From The Time Both Had 30 Million Users
Not to rub it in, but Twitter just isn't growing like Facebook.
This chart from Ian Maude shows how the two social networks' trajectories have split since each hit 30 million users. That is, after acquiring 30 million users, here's the growth for both social networks.
As you can see, Twitter is much weaker than Facebook.
Twitter really doesn't like to be compared to Facebook, and charts like this are why. It's a smaller, slower growing company.
But, that's okay. Not every social network has to be Facebook. Twitter is different, and it's creating a different product.