The only way that people learn about a business is either by accidentally stumbling into them, hearing about them from friends, or seeing an ad for them. All of these things can happen in the online world, and probably happen far more often, just like they can happen in everyday life.
You might walk by a cute store when strolling through town, or find a Facebook page for one when you’re enjoying social media. You might hear about a great hairdresser from a friend when you meet up for coffee, or you may learn about it from a Tweet they posted. As you can see, internet is just as important for promotion as word of mouth.