I get that authors are busy… but so is everyone else.
We all have 24hrs in a day, and if you as an author can’t make time for someone who has taken their time to contact you after spending their time reading your book, then at least hire or assign someone (PR Manager) to do so. Because it’s just rude.
This is where social media helps.
I understand a lot of authors are very reclusive, but if something about your book struck deep in your reader, deep enough for them to want to reach out, there should at least be a platform for them to do so.
A lot of people recommend an official author page or website. And these are helpful resources. But they aren’t always practical. It’s better not to have a facebook page than to have one which isn’t active, where you never respond to messages (I learnt that the hard way).
Some publishers and book distributors such as Amazon and smashwords offer author pages. On Goodreads, you could start a blog if it’s something you’re interested in. And if you pick a couple of sites you know you’ll be active and available on, that is easier to manage, less overwhelming and generally better than having an official site and accounts on every social media platform. Plus, your audience knows exactly where to find you.
P.S. if having all those platforms works for you, then go for it. If not, I hope this helps.