I have held a belief for a long time that prayer is the ultimate evangelistic tool because everyone believes in prayer. You can go up to just about anyone and ask them what you can pray for them about and they will have something for you. They may give you a crass answer, but for the most part, people are not offended by prayer. 24-7 Prayer has taken this idea to the extreme in Ibiza, Spain. The above video is long, but I feel that it can be a great resource to motivate churches to pray for their community.
One side note… we must belive in prayer for this to be effective. What I mean is asking someone what you can prayer for them about mean you will pray for them, not just use it as a transition into the Gospel. Make the transition when it is there, but always pray for the request. Miracles happen when we pray.