Dear Evan Hansen” is shaping up to be this season’s Little Broadway Musical That Could, ringing in more than $1.5 million in advance sales since its Dec. 4 opening, with about $1 million of that coming in the day after the rave reviews hit.

Perhaps even more remarkably, “Evan Hansen,” an intimate musical with a little-known title, proved a box office head-turner right out of the gate, pulling in more than $800,000 from its first seven-performance week. The show’s overall advance is north of $10 million — not quite “Hamilton” numbers, to be sure, but nonetheless a sum that some larger-scale musicals, in bigger houses, might wish they had in the bank.

The groundswell of support, seeded from buzz-building runs at D.C.’s Arena Stage in 2015 and at Off Broadway’s Second Stage Theater earlier this year, seems to stand the show in good stead as Broadway moves into a season crowded with new musicals, several of which are tied to existing properties like “Groundhog Day,” “Anastasia” and “Charlie and the Chocolate Factory.” (Another musical this season that’s started strong at the box office, “Natasha, Pierre and the Great Comet of 1812,” has Josh Groban to help sell tickets.)

“Dear Evan Hansen,” led by Ben Platt in a starmaking performance, centers on a high schooler’s relationship with the family of a troubled classmate who’s committed suicide. With songs by Benj Pasek and Justin Paul and book by Steven Levenson, it’s an emotional, thoughtful show that also has things to say about the ways in which social media helps people both process and exploit tragedy.

All of which makes the eight-actor musical a far cry from the splashier shows that tend to attract instant attention on Broadway. Teens and millennials are a predictably major component of the show’s committed fanbase, given its subject matter and the age of its protagonist. But with two middle-aged mothers featured as prominent characters, the musical also seems to have found a foothold with the older-skewing, generally female theatergoers that make up Broadway’s prime ticketbuying demographic.

“We have a very large, vocal group of followers at this point,” said Stacey Mindich, who leads the producing team of the $9.5 million musical. “What’s remarkable is how engaged they are.”

Because it’s those fans whose enthusiastic word-of-mouth is driving sales, the “Evan Hansen” team is making an extra effort to keep them on side. At the show’s first preview — the performance most likely to be populated by superfans — the audience was given special “Dear Evan Hansen” hats on their way out the door. More recently, some of the show’s most vocal Twitter supporters got free downloads of “Only Us,” one of the songs from the show.

A full cast album isn’t out yet, but it’s on the way. The actors go into the studio this week to record the score, with a release (Feb. 3 on digital, Feb. 24 on CD) lined up from Atlantic Records, which also put out the “Hamilton” original cast recording.