The following statistics represent some of the challenges facing the church in the unfinished task of world evangelism (Ronnie Floyd, Our Last Great Hope (Thomas Nelson, 2011):
As of April 2012, there were approximately 7 billion people on Earth. Approximately 750 million (or about 11 percent) of those are willing to claim Jesus as personal Lord and Savior.
At present, just over 50 percent of the world’s population (or 3.5 billion people) have not heard the gospel and most of them do not have a realistic opportunity to hear the gospel. Here’s another way to look at the challenge of world evangelism:
Of the 11,646 distinct people groups on the planet, 6,734 people groups (roughly 60 percent) contain between zero and two percent evangelical Christians. Many of these 6,734 people groups have no churches, no Bibles, no Christian literature, and no mission agencies who are seeking to share the gospel with them.
If evangelical missions worldwide were able to send one missionary to each group of 5000 people (of the 3.5 billion) we would need 700,000 additional missionaries!
LifeCoach4God 
Stirring article about unreach people,