There are a number of "just to show someone's always listening" things doing the rounds on Facebook - you know the sort of thing, I'll put the kettle on, my door is always open, you can always talk to me.
As a means of trying to suggest that it's ok to talk about mental health, I suppose it's a good thing.
But the idea that a depressed person could talk to just anyone who has a kettle and a packet of chocolate digestives is ridiculous. I know I certainly couldn't, and I've seen a blog about how talking to an untrained listener could in fact be counter-productive, to the point of dangerous.
Even if you want to help a friend who is depressed, you may not have the appropriate skills. By all means, ask them if there's anything you can do to help - but be prepared for it *not* to be making a cup of tea and lending an ear. Like many people, I suspect, it's taken me years (literally) to talk to a doctor: don't ask me if I want to talk about it to you.
A depressed person may just want to hang out with you, doing normal stuff, forgetting if possible, for a short time at least, that they're depressed. And that's probably the best thing for them.