With

Ministering "To" someone is similar to talking "To" someone.
The person doing the talking may or may not actually being doing any good at all.
If you are talking "To/At/For" someone, do you know what they need?  What they think? Who they are?
If you are ministering "To/At/For" someone, they same problems exist.
We don't want to minister "At" someone anymore than we want to talk "At" someone.

Don't minister At someone -- minister WITH someone.

(Note: I jotted this down after watching a video that my sister-in-law posted that was put out by the United Methodist Church on their new missions/ministry campaign.  You can see the video here:  https://www.youtube.com/watch?feature=player_embedded&v=GKBT8mV0CMc )