Frontiers specialises in mission in majority-Muslim contexts, many of which lie in the 10/40 window.
The ministry recently reported that Muslims continue to come to faith through visions and dreams.
They are being baptised and discipled, and some are now helping to establish new churches among their own people.
In one South-East Asian country, a husband and wife team saw very little fruit until their 18 eighteenth year when one woman received Christ and brought her whole family to faith.
The missionaries have now been able to step back and move on to a new area, trusting that the Gospel will continue to spread through the fledgling church.
In a message to supporters, Lewis said his priority focus for 2012 remained the unengaged Muslim communities of the world.
He said the ministry was especially looking at how the Gospel can be planted into family structures and existing social networks.
Mr Lewis said he hoped the Olympics in London would be a reminder to British Christians to pray for the people of the world who have not yet heard the Gospel.
"Represented among the various nation states at the 2012 Olympics will be many of the major families or tribes that the Bible talks about, those who are the intended recipients of the blessing spoken to Abraham and promised to the families of the earth," he said.
"May you know God's blessings this year, and as you enjoy the Olympics in Britain, may it remind you to pray for the many across the world who have yet to hear. Be encouraged that in heaven you will meet families who will say 'Thank You' for being part of bringing the Good News to us."