It's a well-established truth that the easiest way to get attention is to get in the way. Crashing the seamless background against which our lives play out will do it. If you're lucky, you get incorporated into the foreground for a little while. Otherwise, you're a problem; you'll get fixed and the reaffixed.
Now, writing is a great vehicle for getting in the way. We have more ways now for anyone to send text in the direction of hypothetical eyeballs than at perhaps any other time since people first thought to exchange marks on media. But you have to understand "audience" before you can understand any one audience. When you want to move people, having a sense of their ideas, background assumptions, and expectations is oftentimes better than anything you could learn from, say, demographics.
Demographics can get you started, to be sure, but the way people group themselves is always based on ideas and expectations anyway. Better off starting there in the first place.