From Strauss, Encountering Theology of Mission (p. 252):
Church history and the testimony of contemporary missionaries suggest that when the gospel first breaks into a people group or geographic area, the miraculous is frequently present. But the question of how normative such signs and wonders should be for evangelism and outreach where the church is already established and the necessity of signs and wonders for a successful church-planting movement is still an issue of debate among evangelicals.
We must remember that miraculous signs can be duplicated by Satan (2 Thess. 2:9). Furthermore, Jesus reserved his harshest criticism for those who demanded a miraculous sign as evidence of who he was and as a precondition for trusting him (Matt. 12:39). Perhaps the most balanced conclusion is that any biblical theology of mission must put God's power at the center of effective mission and must emphasize that prayer and dependence on God are foundational to the missionary task. It is never wrong to pray for God's miraculous intervention, trusting him to provide it in his time and his way. It is always wrong to demand God's miraculous intervention or to believe that without signs and wonders we cannot be effective in planting the church.