The weekly Serial podcast has captivated America over the past couple months, unraveling a murder mystery in Baltimore that involved a group of high school students 15 years ago. The series has also sparked new interest in podcast advertising—a tactic akin to old-school radio marketing that attracts a slew of tech brands aiming for tech-savvy listeners.

Every episode of Serial, reported by Sarah Koenig, begins with a 20-second callout to email vendor MailChimp. Serial, a spinoff of WBEZ Chicago's popular This American Life podcast, has been downloaded and streamed more than 5 million times, according to The Guardian.

In June, Serial's team asked MailChimp to sign on as the podcast's advertiser. (The company previously worked with This American Life.) After MailChimp sent in the ad’s copy, Serial's Dana Chivvis took to the streets and enlisted passersby to record the now famous ad. One young girl's mispronunciation of "chimp" as "kimp" has since spawned a Twitter account, and the email company even bought the domain mailkimp.com.

"When the first episode aired, that was the first time we had heard the ads—so the girl who can't pronounce [Chimp] was totally spontaneous," said Mark DiCristina, MailChimp's marketing director.

New data from Amobee Brand Intelligence shows people are talking about the ad. From Oct. 3 (the day the show premiered) to Nov. 21, 1,300 tweets mentioned the hashtag #MailKimp. Twenty-three percent of chatter was positive, 55 percent was neutral and 22 percent was negative.

Per the findings, 2,488 tweets mentioned Serial and MailChimp together, equivalent to about 12 percent of the 20,200 tweets related to the email vendor during the same timeframe.

Eighty-five percent of tweets related to MailChimp were neutral, 8 percent were positive and 7 percent were negative.

One of the biggest upticks in tweets about MailChimp happened on Oct. 27, when 4,000 tweets flooded the social site. But interestingly, those tweets were not related to Serial. Instead, the tweets correlated to the launch of MailChimp's Snap iPhone app.

Despite the increase in online chatter, MailChimp is purposely staying away from social media.

"I feel like typically companies would try to take advantage of something like this or be more actively involved with it," DiCristina said. "My point of view is that I feel like it's such a special moment to have with the audience that they're sharing—I feel like if we were to get involved and play along, it would spoil the fun a little bit."

Jumping on the Bandwagon

Two additional tech companies—Amazon’s Audible.com and Squarespace—have also run ads during the program in the past few weeks.

Similar to MailChimp, Audible.com also got involved with Serial after advertising with This American Life.

"As supporters of audio content, the podcasting community is a natural fit for us, and it enables us to reach an audience already familiar with spoken-word entertainment," said Matthew Thornton, senior director of communications at Audible. "The high quality of Serial underscores what the Audible service is all about—bringing superior storytelling to life through the spoken word."

However, the same data from Amobee Brand Intelligence underscores the importance of being first in these kinds of advertising placements. SquareSpace has only received 44 Serial-related tweets since Oct. 3. Audible.com has been mentioned in 31 related tweets.

Serial could be generating more followers for its advertisers, according to data from Engagement Labs. Since Oct. 3, MailChimp has gained 6,891 followers; Squarespace has added 9,098; and Audible has added 2,603.

MailChimp’s DiCristina declined to provide specific numbers but did say that the company has seen an uptick in email signups since the campaign began, but he didn't attribute the new business specifically to the Serial ads. "We haven’t really tried to understand whether it’s driving growth. Frankly, the idea is not for us to drive people from the ad to signing up for MailChimp. It’s more about creating awareness of this company," DiCristina said.

With only three episodes left, Serial has begun asking for donations to fund a second season of the series, which will follow another case. If it is picked up, MailChimp plans to sponsor the second season, even if it is significantly pricier.

"I feel like the lightning in a bottle that we’ve had with this particular ad and the response to it is not something that we are going to be able to recreate if we try," DiCristina said. "If we go into it thinking, 'OK, let’s do this again,' we're just going to fall on our face."