A mere three years ago, Diana Davis published a hands-on book for church leaders titled "Fresh Ideas For Women's Ministry."

When flipping through its pages, she said, one of the first things she notices is a missing word -- Facebook. She needs to rewrite the whole book to cover this reality gap.

"That obvious, isn't it? It's so obvious that we ought to be using Facebook to tell more women about our Bible studies and prayer groups and retreats and things like that," said Davis, who has been married to a Southern Baptist pastor and administrator for nearly four decades, working in Texas and Indiana.

This connection is certainly obvious in America's megachurch subculture and the digital-media pros and market-research consultants who serve it. Davis, however, has focused most of her attention as a speaker and writer on churches that occupy corners in ordinary neighborhoods, not the giant sanctuaries that resemble shopping malls.

Lots of churches, she noted, don't even have solid websites.

Facebook? Isn't it that computer thing all the teens use to waste time?

"Many small churches, or even our medium-sized churches, have nothing -- nothing," she said. "There are people who still do not realize that if you're not online, or if you are not on Facebook, you do not exist for lots of people today. Your church simply does not exist."

The disconnected leaders of these churches should start doing the math, she argued, in a Baptist Press essay offering advice to those who have remained unplugged from Facebook.

First, pastors should request "a show of hands to find out how many church members use Facebook," she said. "The average Facebook user has 130 registered 'friends,' so if just 20 church members use Facebook, that's potentially 2,600 people who could read posts about your church. One hundred members with Facebook could touch 13,000. ...Convinced?"

Once they recognize the potential, religious leaders must learn how to handle life in the parallel universe of social networking. Here are some key rules drawn from work Davis has done with church leaders who have taken their knocks.

-- It's crucial to understand the differences between websites, which users enter on their own seeking information, and Facebook pages, which -- through "friends" links -- can send semi-invited messages into someone's personal "News Feed."

-- "With Facebook," she explained, "you're sending messages to your members, but you're also sending messages to their friends and then, potentially, to their friends and on and on. So it's more aggressive, in a way. You're on offense, not defense."

-- Newcomers should proceed with caution in this casual, yet intense medium. Clergy, she said, "know they have to think before they speak. Now they're learning that they have to think before they click. ... For example, pastors are supposed to use the language well. But if you put something on Facebook that has two or three misspelled words in it, people are going to think that you don't know what you're talking about."

-- It's important to keep messages short, positive and audience-appropriate. Facebook, she said, "is a good place to send out a prayer request, but it's not the place to share details of someone's surgery. This is not the place to talk about the fine details of your church's finances."

-- Know that even simple amateur videos can help. For example, senior adults are more likely to feel comfortable visiting an exercise class if they can watch a short video showing others taking part. It helps to show newcomers what your flock is doing.

-- Social networks cannot replace the human touch of true human networks. Facebook posts cannot replace a covered-dish supper, but they can help bring more dishes and people through the church door.

For example, as soon as news reports began about the earthquake and tsunami in Japan, Davis said her own church rushed out a message urging members and their friends to attend a prayer event. Then volunteers sent the message to other churches and their small-group networks. In short, the invitation "went viral" at the local level.

The result: Instant prayer service.

"That message went all over the place," she said. "We could have never done that by telephone -- that fast, to that many people outside our church. People came from everywhere. ...

"This is real. This is something that more churches just have to try."

Terry Mattingly directs the Washington Journalism Center at the Council for Christian Colleges and Universities.