Where can I write to them?

Good question. The address from the POAAF days on Clint Moore Rd in Boca Raton, FL is long closed, as is the Family Intervention Hotline phone number.

To my knowledge, the fan club address remains
Marilyn Manson
25935 Detroit Rd. #329
Westlake, OH 44145

as it's been since the ACS days. If anyone has differing information, please let me know.