The most popular shows on TV on any given night aren't necessarily the ones that are trending on Twitter.

Take Tuesday nights. The military crime procedural NCIS — the highest rated drama on TV — has owned the Tuesday prime-time ratings since 2008.

But on Twitter, you're not likely to see #NCIS in the trending topics on Tuesday nights. Instead, shows that are much lower in the ratings, such as The Flash, iZombie and Scream Queens, are regularly represented there.

Val Maloney, who writes for MediaInCanada.com, said these shows "might not have a lot of viewers, but the viewers that do watch might be highly engaged with the show and with social media."

For example, iZombie is critically acclaimed but struggles in traditional TV ratings. However, if you check out Twitter trends in Canada or the U.S. on Tuesday nights, you're likely to find #iZombie.

"I think that that might also have to do with the demographic of the people that are watching the shows," she said. "People that are watching Scream Queens and iZombie might be more likely to be also heavy users of social media."

Live-tweeting fuels trends

And those shows are trending, because the audience is talking about them as they're airing.

"There was actually a study that we reported on … from Media Technology Monitor in Canada that reported 90 per cent of millennials go online and watch TV at the same time, so they are multitasking while they're watching TV," said Maloney.

TV networks, of course, have taken notice, and it's not just niche shows that appeal to young people that trend as they air.

Ratings champs like The Walking Dead and Empire encourage their audience to tweet as the show airs. Empire even went so far as to partner with Twitter to display emojis related to the show when its hashtags are used.

And if you PVR the show to watch later, you'll miss out on that live communal reaction.

The Wiz

"Those shows make a concerted effort to be event viewing, so that you don't want to miss it, because if you go online you might see spoilers," said Maloney.

The big winner in both ratings and Twitter mentions last weekend was the live TV production of The Wiz, the musical retelling of The Wizard of Oz set with an all-black cast. Nielsen counted more than 1.6 million tweets about the show posted during the broadcast.

"They're trying to create the social buzz online at the same time that the show is on because of it being a live-to-air show. They want it to be kind of like the Super Bowl… where people want to watch it live and talk about it at the same time," Maloney said.

NBC tweeted clips from the show as it was airing to engage with fans and get more people watching.

They finally made it, see how they got here with "Ease on Down the Road." <a href="https://twitter.com/hashtag/TheWiz?src=hash">#TheWiz</a> <a href="https://t.co/fdenRbqYQC">https://t.co/fdenRbqYQC</a> —@nbc

And while TV mainstays like NCIS may not bother too much with hashtags and posting video clips, for new shows, social media marketing is here to stay.