Of course there are multiple layers to any important question, but the Bible makes it clear that, in the end, God is the One responsible for church growth: "And day by day the Lord added to their number those whom he was saving" (Act 2:47b). God added members to the early church by converting souls.
What are we to do then? Using the early church again as our example: they were meeting faithfully and breaking bread together and praying together, they knew the importance of good teaching, and they were sharing. "A sense of awe was everywhere" and they shared meals with "unaffected joy."
Authentic people being church together is what it's all about.
In a recent conversation, St. Joseph's headmaster, Keith Kiser, in true ecumenical fashion, admonished us to read some of what Pope Francis is saying about evangelism. His thoughts parallel Acts: "We evangelize not with grand words, or complicated concepts, but with 'the joy of the Gospel', which 'fills the hearts and lives of all who encounter Jesus, for those who accept his offer of salvation are set free from sin, sorrow, inner emptiness and loneliness.'”