Here are some good posts on the relationship between missionaries and supporting churches:
What I Want for All Missionaries – Mike Pettengill (GC)
But we want to be loved, and we want to know people are thinking and praying for us. If my team members were reminded that others care and pray for them, they would have strength to endure the hard days.
Missionaries Should Communicate – And Churches Should Demand It – Mike Pettengill (GC) Missions is a partnership. Missionaries and prayers and givers have all been called by God to join together in the expansion of his glory. Your mission team has many members who combine their talents to glorify God in the world. When missionaries communicate what God is doing through the combined efforts of our team, the One who called us all gets the glory.
6 Ways You Can Support Missionaries – Jennifer Su McIntyre
Writing quick emails to your missionary to tell them you’re praying for specific requests assures them that, no matter how isolated they might be, their ministry is being covered in prayer. Being specific about your prayers will help them know you are looking over their requests carefully.