I'd say that it depends on why you are worried about the privacy- is your concern that someone will stalk you or that someone will steal your identity and thus your money or that or do you just have strong veiws about the legality and political issues involved? Each one of them indicates a different house.

Your facebook profile itself is definitely the Ascendant and 1st house - it is you for all intents and purposes in this context. The clue being in the name 'Face' book.

As far as facebook normal use is concerned ( though in this question's context it is not relevant) , again depends on what the individual uses it for -I'd go with 3rd for those people who just have their current school mates on there -9th for those who have a a lifetime of international contacts on there and so on.

The three things I've come to the conclusion about with horary is that:
i) the key is the exact state of the questioner and their question - that leads to the exact definition of the significator of the quesited.The cookbook quesited house and/or significator ( whether traditional or 20th C) is a guide and the right one can always be worked out by picking apart the question and using the real core meanings of the houses that have existed since the first authors.

ii) Pretty much any question of real long term importance to the questioner will involve the angles ( either a relationship -7th or a decision indicating sucess or failure -10th) or the 2nd or the 6th houses.

iii) If in doubt follow the moon ( and the sun moon phase)

Goca wrote:

my interest being in which house Facebook would belong to in general.

I would say it is 11 house matter:"In modern astrology it is said to rule the wider social circle of acquaintances and groups and those who share our aims."

Goca is correct, for all its many flaws ultimately its about friendships and belonging to groups, also its used for radical groups and meetings so must fall into 11th/Aquarian concerns.

G

Maybe look for a connection between 11th (Facebook) and 1st (your profile) and maybe the 10th (public image/reputation). Afterall, Facebook is a social network and the "friends" and "groups" you have chosen to interact with, which fits with the 11th. Your profile is you and that is always the First, and of course, you can't get anything more public than Facebook, hence the 10th. If there is reason to doubt about continuing on with this "club/social network" then there must be some discord between these rulers.

Just a thought.
Tracey