The true mailing address as listed on the website FAQ/Contact Us/Right Sidebar is:

If you'd like to send us postal mail, you can send it to:

Virgin America Guest Care
P.O.Box 4271
Burlingame, CA 94010

I kindly suggest that if your friend has something to complain about, he/she start with Guest Care and see if they can obtain resolution before going directly to the CEO. I can assure you that the CEO is made aware of all complaints, organized by root cause on a regular basis and is involved in decisions on solutions to guest issues where the matter is of significant importance.