Well, the original one, which you can find out about here
, is over - but - eh - why wait for a specific day to be declared for this? Is there someone whose work you absolutely love, someone who might be a new writer, or an established writer who hasn't had something new out in a while but whose older stuff you still adore, or anyone whom you've just "discovered" having previously known nothing about them - trust me, writers are real people and they're cut off from seeing the response of readers by virtue of the fact that those readers might live in a different town, or state, or country, or CONTINENT from the author him or herself - writers LOVE hearing from readers, there's an electric joy in having someone write to you and say, "hi, we've never met, but I just read your book and I thought I'd write to you and tell you how much I liked it".
You can always write to your author in the traditional wise, via their publisher, who should forward such missives to where they need to go; but these days it's even simpler than that, because a vast majority of us scribblers have blogs, or websites, or other ways in which an email can be obtained - and you don't even need an envelope and a postage stamp. And you have no IDEA how wonderful it is to find a nice note tucked away in your inbox, telling you that your words reached somebody, that someone else loved your baby, that what you are doing has meaning and value and, in some manner, affects another human being in measurable ways.
In fact, I am going to go out and pen e-missives to half a dozen authors whose email or blogs I have access to. You don't need to have a special day for this - making another human being feel warm and fuzzy and good about themselves is a good deed at any time. Go on, do likewise. Make the day of some isolated word-wright, sitting there by candlelight and dreaming up new worlds for y'all to go journeying in. Go on. Do it. Do it now.
Tell an author you care.