Good types of support are:
Remain calm no matter how much rage you might have, because expressing these emotions to the victim may cause the victim more trauma.
Encourage the victim to receive medical attention, even if they don’t report it to the police the victim is entitled to a free medical exam which can provide preventative medicine for various issues as well as indicating any type of internal injuries.
Give the victim back control. Control to determine the next step, especially since control was taken from the victim through the assault.
Let the victim express feelings when they need to, without your opinion. If they choose to remain silent, just let them know you will be there for them and ready to listen when they are ready to talk.
When and if they do talk it is very important to maintain confidentiality. It is up to the victim to decide who they want to know about the assault. If you break their trust this can be very detrimental to your relationship.
BELIEVE the victim and let them know that it was not their fault!
Encourage counseling. Let them know that we as individuals are not “wired” on how to deal with rape by ourselves and to seek help from professionals who are.
Seek counseling for yourself in order to address the feelings you have without bombarding the victim right now. The victim needs to concentrate on getting themselves better before worrying about everyone else. Then after time with counseling you can decide when and what to discuss with the victim, if you feel it is even necessary at that point.