One of the biggest advantages to being a collegiate a cappella group is the fact that with the school affiliation can come school benefits. Sure, this means performance spaces, a youthful audience, the potential for faculty guidance, a large pool of new people coming in each year from which to recruit new members.
It also means a school website.
School websites are visited by a full range of students, faculty, staff, and prospective new members of the community. This means is that, even if someone isn't looking for your group, or a cappella at all, if you can establish a presence on the site, you will reach a far greater audience than you probably would by an intentional means.
But how do you establish such a presence?
Lots of schools have an events calendar that list everything from cultural nights to awards ceremonies to on-campus movie screenings. Make sure each and every one of your shows finds a place on this calendar so people who are openly looking for something to do on a Friday night know that your performance is an option.
Many schools also feature student organization profile pages. In my experience, this is one of the most underutilized tools available to any collegiate group. So many students--particularly new ones--will peruse this section of a school's website when they're looking for ways to get involved or things to do. Take advantage of this by updating such a profile at least once year; ideally as frequently as you have any real changes in terms of contact people, website links, etc.
If your school's website has a newsfeed, or otherwise publishes news shorts from the college community, don't forget to take advantage of that either. In addition to current and prospective campus community members, it's not unusual for alumni to make use of such a resource to keep abreast of what's going on at their alma mater. Alumni can boost attendance numbers at shows, and, if they're faring well in their post-collegiate careers, may even have money to spare to help fund your next tour.
Your school's website should be one of the most fundamental pieces of your social networking toolkit. Don't let that opportunity slip.