For decades, the song of the summer would emerge each year following a pattern as predictable as the beach tides.

Pop radio would get it rolling before school let out, and soon the song — inevitably one with a big, playful beat and an irresistible hook — would blare from car stereos everywhere. Then came prom singalongs as the song finally became ubiquitous around the Fourth of July. In 1987, it was Whitney Houston’s “I Wanna Dance With Somebody.” In 2003, Beyoncé’s “Crazy in Love.”

But the success of this summer’s hit, Carly Rae Jepsen’s cheerfully flirty “Call Me Maybe,” shows how much the hitmaking machine, as well as the music industry itself, has been upended by social media.

Only a year ago, the charts were dominated by stars who had come out of the old machine of radio and major-label promotion: Katy Perry, Rihanna, Adele, Maroon 5. This year’s biggest hits — “Call Me Maybe,” Gotye’s “Somebody That I Used to Know” and Fun.’s “We Are Young” — started in left field and were helped along by YouTube and Twitter before coming to the mainstream media.