Customer respect is of course #1 - but an aspect about this to consider is
what are you respecting?
Many customers of online adult content appreciate anonymity. Are you respecting this if you approach them somehow?
To refine what you're saying:
Although direct email might not work, newsletters function as customer-approved means of contact. Those who won't submit their email addresses don't want you to approach them in any way - or rather, don't want to have a record anywhere of their "contact" with your site (forget Snowden and the NSA - think of the wife!).
Think also of the huge deleted/junk/spam/whatever folder of most freemail providers now - who the hell ever purges those unless they unrealistically must?
However, having a separate contact form in your members area, with a corresponding inbox section, can help invigorate the personal interaction with members/customers (think social network applications, bulletin boards, something along those lines).
Depending on whether you have a solo site or multi-model site, you could/should have a drop-down referring that customer's communication targetted specifically to their "favorite" - or by other subject/topic/niche.
In the best of circumstances, this could be replied to by that "favorite".
This could be an option offered only to those who need anonymity.
Those who don't can use standard email-reply, newsletter or other interactive responses... like paid custom-fetish recorded video replies (online or downloaded upon request) or just a drop-shipped custom photo or basic calendar....
I'm spitballing here so bear with me
If you're big enough to require direct phone support, I definitely agree with having direct, "personal" support (from past experience with all kinds of Indians who are trained to say stuff like "So how about that [insert local sport or weather phenomenom]?" while they're waiting on more specific technical responses...
Definitely agree: do not spamblast the same message across multiple social platforms; I've blocked or removed contacts across many who either repeat the same shite over and over or constantly post consumer-oriented stuff to industry-oriented forums/groups/you-name-it.
To know what other/other-kinds of sites customers like, run members/social area polls.
To reach out to those who request absolutely anonymity (and who clear cache, offline files, cookies, etc. because of other people's access to their computer), grant customer loyalty specials, discounts or bonuses targetted at them specifically and keep a list of users who don't submit email addresses vs. those who do - and if you can try to provide separate access/tours/welcome-paths between each.
Much of that would be software/programming steps, which are not undoable, just additional time/resource/expense factors.
There, I seem to have spit the last ball :P
OH except - (post)Merry Christmas, Happy New Year and generally happy holidays to all!
:D