Last week, author Penelope Trunk wrote in the Guardian about what she considered to be her mainstream publisher's incompetence at marketing in the modern age. Commenters on the article had little sympathy with Trunk, for shameless marketing of her (ultimately self-published) book, or for her tone. These were a block to seeing the potentially valuable points she raised: that publishers are floundering in the digital sea, and failing to develop marketing plans that make the most of online opportunities. But was she right?

It has always been the case that people think things are worse now than ever. More books are published, and space in mainstream newspapers' books pages is under threat: more into less doesn't go. With the ongoing decline of independent bookshops, conviction-based bookselling is replaced by a numbers game, in which Nielsen BookScan data is all-important. The country's remaining high street chain, Waterstones, has cancelled the standard industry practice of returns, where unsold stock could be sent back to the publisher. This seems to have had the effect of dramatically reducing its orders on new, untested titles. Store browsers can't discover a book that isn't in stock.

Despite Trunk's brickbats, publishers are not blind to the challenges in – and opportunities for – selling books in an increasingly fragmented media. Many value bloggers, whose coverage they see as a cross between a mainstream press review and the much-desired word of mouth that drives big sales – and all for the cost of a proof copy. Most publishers also have their own social media presence. But these Facebook pages and Twitter accounts are tweeting to the choir – Trunk rightly noted that, to most people, publishers are not household names. Similarly, it's always bizarre to see an author retweet praise of their books from admiring followers, to other admiring followers. Perhaps the best thing an online presence can do for the midlist author is hang on to existing readers while writing the next book.

For publishers, marketing depends on the budget, and for most new books, there is no budget, so the task falls to the publicity department. The buzzword is "discoverability". But there is no proven way for publishers to find the right readers through digital strategies. This means that for most titles, time devoted to working on a digital strategy could be better spent in supporting a traditional campaign with digital detail: tweeting reviews, putting giveaways on Facebook, getting the metadata right on the website.

So if publishers and authors are limited in what they can do for a book online, who is left? They want to harness word of mouth, and power lies collectively in the independent readers – you and me. Can we make a difference when the bookselling world is full of outlets, online and off, which primarily sell what already sells, or can be related to a proven success ("It's Fifty Shades of Grey meets Harry Potter!")? If social media has inspired a new age of grassroots political activism, why not literary activism, too?

I decided to test this idea, with a new book that seemed to me exactly the sort of thing that gets missed by book chains uninterested in the new and different. The book is Hawthorn & Child, the new novel by Keith Ridgway, a writer whose name has not troubled most households. I read the proof and thought it extraordinary: surprising, dazzling, affecting and upsetting. Another early fan, better read than me, said that one section was "a masterpiece possibly on a level with Kafka's In the Penal Colony". But where's the angle in being merely a great writer? How many broadsheet profiles did Kafka get in his lifetime?

Hawthorn & Child's publisher, Philip Gwyn Jones at Granta, "had to pluck up the courage to acquire it" as he "had concerns about how hard it would be to sell". It is a novel in unresolved stories: "Holding the reader down and anti-climaxing all over their face," as one source memorably put it. Yet it is not a "difficult" book: it has oodles of narrative drive and would, I thought, be widely loved if widely read. My motive was a sort of altruism – wanting others to get as much pleasure from it as I did – that disguised selfishness – wanting it to do well enough that the author would have the means and time to write more.

So as well as posting a review of the book on my blog when it was published, I went into guerrilla marketing mode on Twitter, and risked the wrath of people who have let me into their timelines, by tweeting about it incessantly on publication day, and intermittently thereafter. As people began to follow my advice and read the book, I retweeted their comments, all (so far) positive, and many matching my own enthusiasm. "One of the best books I've ever read," tweeted one reader. "If it doesn't win every literary award going we should riot," said another. My praise was picked up by at least one prominent tweeter, too.

But what effect did all this have? It worked wonders for my blog stats, and the Amazon sales rank rose from the tens of thousands to the single thousands, but it wasn't until a review was published in the mainstream press – in this paper, and the only review the book has had in the UK press so far – that the Amazon ranking broke the top 500. And behind all this, there was a digital strategy even before the book was published. Granta published a teaser story, an offcut from the book, in advance, and at a good time (it's about a terrorist attack on the London Olympics), as well as an extract on their website. Further back, Ridgway's agent, David Miller, had sold individual parts of the book to homes as prestigious as the New Yorker, helping build anticipation for the finished work.

What I do know is that my excess exuberance has made the author at least a few new fans. I hope the enthusiasm will continue to trickle down. Is there a model in this? Who knows, but if your favourite book isn't getting coverage anywhere else, then you have to spread the word yourself. Ask not just what the author can do for you, but what you can do for the author.