Pray regularly for your missionaries. As a pastor I wanted my church to hear me praying for our missionaries often as we prayed together.  I would also encourage them to do the same.  Do you have a time when God’s people share prayer requests?  Why not include your missionaries?  In fact why not after having read their prayer letters yourself you include some of the prayer requests they have mentioned in their letters as well?   I am sure they not only covet your prayers, they are also very grateful for the prayers as well.   After all, we are co-labourers.