Reading a novel is, for many (myself included), a personal experience.
We get lost in a story, experience pain, loss, anger and victory along with characters that we (hopefully) come to care about, as though they were real. And when that experience ends, we miss our new friends and want their fictional lives to continue. Like, now. With the characters and plot still fresh in our minds we *might* tell a friend about it. You know the one. That rare breed who reads novels as voraciously as you do. And then…
The subject might come up again six months later, when your reader friend finally gets around to reading the novel, but your excitement is waning because you’re still waiting for a sequel that may or may not be on the way. A year passes. Then two. What is taking the author so frikkin’ long to write the next book?! It was amazing. How could there not already be a sequel?
Eventually you decide to take matters into your own hands and e-mail that author. He/she probably won’t reply (I will), but maybe your e-mail will spur them into action.
I get these e-mails. A lot. For Jane Harper. For Refuge. For Flood Rising. I even get them for books that were never meant to have sequels. And my response is always something like this: (Insert book title) needs to sell better before I spend a LOT of time and money writing and publishing a sequel. The best way you can make that happen is to post a review on Amazon.