I haven't put a lot of thought into this yet, so this is a, you know, thought in process. Consider the following utterances:
I saw it on my Facebook.
I've posted a blog about that.
I read this great Tumblr ...
There's a Wikipedia about it.
I think it's clear that these are synecdoches of one sort or another, but there is some subtlety to their usage.
Facebook
Let's start with Facebook. Many times I've heard people refer to my Facebook:
A guy on my facebook just proposed ... [
source]
An Open Letter To The Women On My Facebook Whose Husbands are Policemen [
source]
What you might expect here is something like my Facebook wall or feed or page or timeline. But there are other usages where people might be eliding account. So by logging into my Spotify, my Facebook was reactivated without my knowledge.
I still haven't logged on to my Facebook [source]
Since I’ve had a Facebook, I think I got one in 2007, that’s a total of 1,274 hours, or 53 DAYS. [source]
I've had my Facebook since third grade. [source]
Comment (on FB): My Facebook is basically all about life's small dramas.
Next comment: Everyone's facebook is.
I've heard this usage ("my facebook") from my own kids (mid-20s).
Blog
It's not hard at all to find instances of people using blog to mean something like blog entry:I posted a blog today [source]
I have a MYSPACE account where I posted a blog [source]
I like the second example because the writer uses uses blog in a meronymic way, but doesn't do the same for MySpace. It wouldn't be unreasonable to expect to see I have a MySpace here, but we don't.
Update: I found an example of this in a surprising place, namely on the mobile page for Dictionary.com.
Tumblr
Probably the most common example of a synecdoche that I hear these days is my Tumblr, representing (mostly) my Tumblr blog:just added a music playlist on my tumblr :D
Finally! I added music to my tumblr.
[source]
Wikipedia
I was actually inspired to post this because I overheard someone at work say There's a Wikipedia about that. It was the first time that I recalled hearing an example of this elision with Wikipedia specifically.
So, more another time when I've thought about this further and have more examples. And btw, I go back and forth on whether these are examples of synecdoche or whether it's some other phenomenon besides simple elision.