To build an audience for art, particularly live performing art, you've got to make it feel like a must see event.
Other forms of media and entertainment do not have such a high bar. A movie has plenty of opportunities to snare audience (in the theatre, on DVD, on demand). A TV series has similar options.
But the live arts happen in a specific time and place. People have to drive, pay to park and for admission. People don't do those things for events they "kinda want" to see or are "just considering".
People have to be extremely motivated to see the arts and generating excitement is a vital part of that.
How do you generate excitement?
One (extremely strong) way is by building authentic relationships with people. Another way is through the effective use of video, blogs and other content. For an example of that, take a look at this. It's a link to a website my day job built for an upcoming production. It includes music, videos, even an online quiz.
Why go through all the effort to build the site?
The hope is that as people listen to the music, or take the quiz, their excitement level will grow. We tried to give people enough content to move the event into the "must see" category.
The point of every marketing tool at your disposal, PR, social media, print advertising, posters, etc. is to spark a real emotion out of people. Get them interested. Get them excited. That's when they will come.