Goodreads members represent a small portion of all book buyers, and it is not immune from some of the politicking that goes on elsewhere — authors are not prevented from reviewing their own books, for instance. But advocates consider this acceptable because readers can choose their own reviewers.

“Because Goodreads is not a publisher or retailer, people feel that the information is not getting manipulated,” said Amanda Close, who runs digital marketplace development for Random House. “People trust them because they are so crowd-sourced and their members are fanatics. You can’t buy a five-star review there.”

Ms. Hettler, who trains employees at a T. J. Maxx warehouse, started her own group on Goodreads, the Next Best Book Club, which now has more than 10,000 members. She has become so well known that not only does she never run out of book recommendations, but she is also courted directly by small publishers like Graywolf Press and Artistically Declined to promote their authors.

“I am trying to use my platform to spotlight the underdog,” she said. “My reach is limited, but I know what will speak to my audience, and when we pitch a book, we clearly see an uptick in people who say they are going to read it.”

Goodreads.com was founded by Otis Chandler, grandson of the last family owner of The Los Angeles Times, and the woman he later married, Elizabeth Khuri Chandler. They met after graduating from Stanford University.

Trained as an engineer, Mr. Chandler was always interested in starting his own social media company, and his first job included working on a dating site. Ms. Chandler trained as a dancer and worked as a writer and editor. But what they shared was a passionate love of books, and they quickly realized that books bound others as well.

“Books are one of the strongest social objects that exist,” Mr. Chandler said in an interview, “so lots of people are innately willing to talk about and share them.”