• The film adaptation of John Green's "Paper Towns" stars Cara Delevingne and Nat Wolff.

The film adaptation of John Green's "Paper Towns" stars Cara Delevingne and Nat Wolff. (Photo : Facebook)

"The Fault In Our Stars" and "Paper Towns" author John Green, 37, and the "Divergent" series writer Veronica Roth, 26, joined Forbes' list of top three highest earners.

Book sales are boosted by the film adaptations of their bestsellers thanks to the global marketing blitz targeted at teens and young adults, raked in huge profits at the box-office.

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Green's and Roth's books offer a thrilling ride, particularly for young adults who can relate with the angsts- and adventure-filled journey of their protagonists. While Green's storylines delved on teenage drama and romance, Roth's focus has been on young rebels amidst a dystopian societal backdrop.

Green's book "The Fault In Our Stars" became a New York Times Bestseller; it eventually became hot Hollywood material that catapulted its stars Shailene Woodley and Ansel Elgort to full stardom.

Book sales of "The Fault in Our Stars" soared to 3.5 million copies in the United States alone in 2014, while the film adaptation made gross global earnings of $307 million, a hefty sum given the allotted $12 million budget. This accounted largely for Green's estimated earnings increase of  $17 million over the 2014 figure, Forbes reported.

Roth, on the other hand, had climbed to the top three spot alongside the novelist Danielle Steel. Roth sold a whopping 6.7 million copies of the first part of her "Divergent" series a year after its publication in February 2012, the website Divergent Society reported.

Crime writer James Patterson remained unshakable in the top spot as the highest paid author.