My dad was a missionary church planter in Nigeria. He pioneered an area of north eastern Nigeria where there had never been a missionary. It was a unique experience to be “first in” to give the gospel to a remote people. They responded. Churches were established.
One of the practices of those churches was to call out every member’s name during the Sunday morning service. Each person would then stand and give a number in front of the entire congregation. The number they called out reflected the amount of people that they witnessed to during the past week. That kind of accountability is probably too much for the average American congregation. But imagine what it might do to evangelism if we had some public means of encouraging one another.
The reality is that unless there is a weekly opportunity for people to talk about their evangelistic efforts, it will probably decline. It doesn’t need to be quite as public as the church in Nigeria but it could simply be a point of conversation in a small group or Sunday School class. Each week, take 10 minutes to talk about what evangelistic experiences people had the preceding week and what they are planning to do in the coming week.