Joining the group that says to use the real names. Unless it's something in the far-away future, I see no reason why not call it Facebook and YouTube.
I definitely support using the real names. I used Facebook a lot in A MIDSUMMER'S NIGHTMARE, actually at the request of my editor (originally it was not an online issue, but making it Facebook bullying made it more real.) It is possible it'll date your book down the road, but with movies like the Social Network out there, people won't forget FB for quite a while. And YouTube is so big, I imagine it'll be the same way.
I mean, I have seen A LOT of people make fun of the scene in Twilight where Bella looks up vampires using her "favorite Internet search engine." It's Google. She's using Google. Everyone knows she's using Google.
The name of the Facebook/MySpace mashup on this one ABC soap called One Life to Live was called MyFace. It always seemed kind of hokey to me.
I feel like it's only in YA that everyone is so concerned with 'dating' their work. In most adult fiction, it seems like there is a specific, named time period so it's okay to mention websites, movies, music, current events of the time, etc.
If you're writing contemporary, please don't worry about "dating" your novel.
There's nothing wrong with your story taking place in 2015.
I feel like it's only in YA that everyone is so concerned with 'dating' their work. In most adult fiction, it seems like there is a specific, named time period so it's okay to mention websites, movies, music, current events of the time, etc.