(UNDATED) A week ago, I had little firsthand knowledge about Facebook and other “social networking” tools.

I had read a lot about Facebook, Twitter, MySpace and LinkedIn. I had opened accounts. I occasionally clicked “Yes” when friends invited me into their networks.

But otherwise, I had little direct experience with this burgeoning Web phenomenon, in which people connect with each other through groups, discussion boards, resume sharing, mass postings and one-on-one dialogue, as well as pages describing their lives.

Then I created a Facebook group for readers of my “On a Journey” writings. Within a week, 40 people had joined the group — men and women, young and old, veteran “early adopters” and tech novices, people who jumped right into posting entries on the “wall” and in “discussion boards,” and people who had no clue what those terms even meant.

I realize that 40 members is a far cry from Facebook groups boasting more than 1 million members, or the massive crowd “following” President Obama on Twitter, or the 1,500 members of a British group discussing worms.

But it has surprised me. I had no idea so many people, other than teenagers, used social networking. MySpace is slipping, but Facebook has moved into the top 10 most-visited Web sites, with its biggest growth said to be among the over-30 crowd.

I discovered that a Virginia pastor uses Facebook to connect with his church’s small groups, and that one Facebook venture claims 20,000 churches use its services to stay connected between Sundays.

Social networking has gone way beyond idle musings. LinkedIn is helping newly unemployed professionals network for jobs. Twitterers were among the first to report a jet down in the Hudson River. Anti-government activists in Moldova used Twitter and Facebook to organize their recent demonstrations against police abuse that was first witnessed via YouTube.com.

In fact, social networking is such a potent vehicle for free expression that autocratic governments routinely shut down leading sites, lest the people find their shared interests.

As Christians celebrate the days in which one woman’s discovery of an empty tomb opened the way to a worldwide movement, we should note that our faith initially spread by word of mouth.

Before ambitious institution-builders took over with sword, legalism and threats of eternal damnation, we were, in effect, a “viral marketing” phenomenon of one person telling another.

That is still what we are. Even in an age of powerful mass media, the most effective Christian witness happens by word of mouth. Within a month of reaching New York City, five people had told me about a 5,000-member church that has no signs, no advertising and no building of its own.

Churches, like restaurants, grow as one satisfied “customer” tells another. It’s also how they fail, as the word goes out: “All they do is fight,” “it’s all money,” “boring, boring.”

On this level playing field, historic denominational labels count for little. Treasured assets like beautiful facilities, excellent music or a noble history cannot create positive “buzz.” In the end, it’s about substance, not show. If a congregation feels itself losing ground, it should examine what, if anything, the social networks say about it.

We Christians can compete in this marketplace of networks, but only on the basis of current substance, not historic show, and only when our people have an inspiring story to tell.

(Tom Ehrich is a writer, church consultant and Episcopal priest based in New York. He is the author of “Just Wondering, Jesus,” and the founder of the Church Wellness Project, http://www.churchwellness.com. His Web site is http://www.morningwalkmedia.com.)