You can write to Miley at the following addresses but Miley is a really busy person so she may not reply. Also it is advised you send a envelope with your address on so if she does reply its quicker and easier for her.

Miley Cyrus
CESD Talent Agency
10635 Santa Monica Blvd
Suite 130/135
Los Angeles, CA 90025

Miley Cyrus
c/o The Disney Channel
3800 Alameda Ave
Burbank, CA 91505

Miley Cyrus
c/o BRC Spirit
P.O. Box 1206
Franklin, TN 37065
USA

Miley Cyrus
Morey Management Group
9255 West Sunset Boulevard
Suite 600
Los Angeles, CA 90069-3303
USA