Operating on the assumption that lapsed churchgoers would attend a service at the encouragement of a friend, several Christian groups and denominations have organized National Back to Church Sunday.

The organizers announced Wednesday that they had met their goal for participating churches for the day that is scheduled for September 15.

More than 20,485 churches have registered to participate at the event website thus far, with more expected, the National Back to Church Sunday campaign says on its website.

"We believe there are millions of Americans who would welcome an invitation to come back to church, or who might be a bit curious about attending church for the first time," said Scott Evans, founder and CEO of Outreach, Inc., which provides church communications resources that helped launch the initiative.

"Whether most Americans believe in God and have an interest in spiritual things isn't in question. The question is what are they going to do about their beliefs and what are believers going to do to make people feel welcome."

This figure exceeds the registration for the 2012 event by 30 percent. Two million Americans are expected to be involved in National Back to Church Sunday.

Since the initiative began in 2009, National Back to Church Sunday has seen increased success. Some 3,800 churches participated in 2010.

"Like any target, it's exciting to hit the number, but the number is the symbol for the real purpose of the goal," noted Evans.

The back to church program was endorsed by Lee Strobel, best-selling author of The Case for Christ and The Case for Faith.

"Seven out of 10 unchurched people would visit a church if a friend invited them. What are we waiting for?" said Strobel. "The church offers hope, grace, truth, joy and the message of eternal life - all of which we want our friends to experience. Let's take a risk and prayerfully offer an invitation."

Other celebrities who have endorsed the special day are baseball star Josh Hamilton and Bethany Hamilton, subject of the movie "Soul Surfer."

Participating churches are making special plans for the event Sunday, holding special services and encouraging their members to invite someone to come with them.

The sponsors of National Back to Church Sunday say that only two percent of churchgoers invite someone to attend with them in a given year.

Yet according to Thom Rainer of event sponsor Lifeway Research, 41 percent of Americans would come to church if they were invited by a friend.

John Upchurch, senior editor of Bible Study Tools and Jesus.org noted on the Christian webzine Crosswalk that the problem of the "The Nones", people who claim no religious affiliation, has been a "tour de jour" of Christian researchers like Lifeway and Barna.

The Pew Research and Public Life Project reported in 2012 that the "The Nones" were on the rise in the U.S., with 20 percent of the public –and a third of those under 30--indicating that they were not affiliated with any religion.

Upchurch says that nearly 20 percent of "The Nones" do not know a Christian who could dispel misconceptions they have about the Church.

"Even still," he said, "younger Nones have expressed greater interest in God than their parents."

In his post, Upchurch quoted research by Thom Schultz, author of a new book called "Why Nobody Wants to Go to Church Anymore," who noted that Nones think God is irrelevant, but would like to believe that there is a God who cares for them.

"The church offers hope, grace, truth, joy and the message of eternal life—all of which we want our friends to experience," said Strobel. "Let's take a risk and prayerfully offer an invitation "

To help encourage churches to promote and church members to invite, National Back to Church Sunday has ready to use materials on its website. Free materials include a roster listing publicity materials tips for using social media, and information about using the event Facebook page and YouTube channel.

Those wanting to attend can also find a church in their area on the website.