Two ways to grow:
Broaden your audience focus. Facebook is the best example. Facebook jumped from Harvard to ivy-league schools, to all almost all educational institutions to just over everyone in just over two years.
Double down on your existing audience. StackOverflow and Kaggle are good examples. Begin with one functional purpose you can help your audience with and gradually find more and more ways to be useful.
For most of us, I’d go with the latter.