Lindsay Dunn was upstairs in her bedroom finishing up her homework when her phone began “buzzing nonstop.”

The Hampton Bays High School sophomore was receiving notifications for the hundreds of new followers subscribing to her YouTube channel.

They had all found the 15-year-old from a link shared by The Chainsmokers, a popular dance music duo whose recent single “Roses” has been on the Billboard Top 100 for 23 straight weeks.

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Earlier this month, the group shared a clip from a video of Dunn covering two of their songs, “Roses” and another recently released single, “Don’t Let Me Down,” on their Facebook page.

Within hours the clip had received thousands of comments and likes. As of Thursday morning, it had been viewed nearly 2.7 million times on Facebook.

“I completely freaked out. I definitely didn’t expect it,” said Dunn, who got her start in music as part of the choir at Christ Our Saviour Lutheran Church in Hampton Bays, where her grandfather’s a pastor.

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Dunn recorded the video in mid-February at Loft Sound Studio in Plainview, with the help of producer and voice coach Donnie Klang, who won a contract with rapper Sean “Diddy” Combs’ record label in 2007 after appearing on the MTV reality show “Making the Band.”

Klang says Dunn came into the studio wanting to record a simple cover of “Roses,” but he encouraged her to try splicing the song with a “more current” single.

After a couple days of recording, Dunn posted it on her YouTube channel.

She was praised by her friends and her modest YouTube following for the video, which uses a clever camera trick that makes it appear as if the teenager’s singing with herself onstage. One Dunn appears stage left in a floral-print blouse belting out “Roses;” the other in a dark sweater sings “Don’t Let Me Down.”

The video had just a few hundred views before it was shared by The Chainsmokers, who praised Dunn in their post: “Props for the creativity on this one! This sort of stuff is one of the coolest things about being an artist and having fans like you guys . . . [seeing] you all reinterpret our stuff and make really amazing things is so cool!” the group wrote.

Others chimed in. “Get her as vocals on a track!” one user wrote in response to the duo. “Goosebumps all over my body!” another commented.

Since the video went viral, Dunn says she’s gotten several requests from musicians and DJs asking her to record with them.

She hasn’t yet decided whether she wants to work with other artists, but says she’s in the process of recording another mashup that should be posted in the coming weeks.

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“I’m excited about the attention the video’s received,” she said, “and even a little hopeful that this could lead to something bigger.”