Gauging the popularity of a TV show a few years ago was simple. Nielsen sent out overnight ratings the next day and that was it.

It's now much more complicated.

First of all, 47 percent of households use DVRs, according to a new report late last year from the Leichtman Research Group. About 36 million people are now Netflix subscribers. There's on-demand viewing. There's online viewing, which isn't even measured by Nielsen. Fox now offers "projected" ratings the day after a show airs including DVR usage.

Social media is another factor when it comes to viewer "engagement," a term TV executives like to use. Twitter has helped fuel popularity of some shows, especially live programming (sports, award shows), reality competition shows that replicate sports shows, cheesy dramatic reality shows and the occasional scripted drama. The shows also work Instagram, Tumblr and Facebook. The philosophy now is grab them where-ever you can!

Here are four shows that have used social media to fuel their rabid fan bases:

Returns for fourth season Thursday night at 9

What it is: A juiced-up drama featuring a D.C. fixer and perpetually crazy presidential intrigue.

Average viewership: 12 million

Facebook likes: 2.6 million

Instagram posts: 744,000

Average tweets during an episode: 405,000

Why it works for social media: Creator Shonda Rhimes packs in so many ridiculous plot twists and soundbites into each episode, it's easy to miss what's going on if you step away for even a minute or two. Her fans love quoting the nuttiest lines in real time on Twitter, then post amusing memes - video tidbits with often wry commentary on them.

Ben Blatt, ABC's executive director of digital strategy, said the show encourages actors to live Tweet and many do so every week. This year, they are experimenting with Snapchat (where videos and photos disappear after a few seconds) because that's where young folks preside. They also shoot a lot of video and photos during production and embargo those moments until the episode airs on places such as Instagram. "Fans love that inside access," Blatt said. "And we make sure they are more like smartphone photos than professional. It feels more authentic."

PRETTY LITTLE LIARS - “Pretty Little Liars: We Love You To DeAth” - The town of Rosewood is a perfect setting for things that go bump in the night and this Halloween ABC Family’s “Pretty Little Liars” will give its devoted fans an inside look at the show with interviews with PLL cast and crew. The fan special “Pretty Little Liars: We Love You To DeAth” will air on Tuesday, Oct. 21st at 8 PM ET/PT, as part of ABC Family’s “13 Nights of Halloween.” (ABC Family/Eric McCandless) TROIAN BELLISARIO, SASHA PIETERSE, LUCY HALE, ASHLEY BENSON, SHAY MITCHELL PRETTY LITTLE LIARS - “Pretty Little Liars: We Love You To DeAth” - The town of Rosewood is a perfect setting for things that go bump in the night and this Halloween ABC Family’s “Pretty Little Liars” will give its devoted fans an inside look at the show with interviews with PLL cast and crew. The fan special “Pretty Little Liars: We Love You To DeAth” will air on Tuesday, Oct. 21st at 8 PM ET/PT, as part of ABC Family’s “13 Nights of Halloween.” (ABC Family/Eric McCandless) TROIAN BELLISARIO, SASHA PIETERSE, LUCY HALE, ASHLEY BENSON, SHAY MITCHELL

Credit: Rodney Ho

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Credit: Rodney Ho

“Pretty Little Liars” (ABC Family)

In the middle of season four but on hiatus, with a Christmas special pending

What it is: Four women whose lives were overturned when their "queen bee" leader supposedly died. It's based on a book series by Sara Shepard.

Average viewership: 3.4 million

Facebook likes: 14.4 million

Instagram posts: 2.7 million

Average tweets during an episode: 675,000

Why it works for social media: In 2010, the author's existing Twitter fan base jumped on the TV show. "Our relationship with social media was born in a very organic way," said executive producer and showrunner I. Marlene King. "We didn't seek it out."

Now when the show airs, “we have this giant social media Twitter party,” King said. “I’m always on when the show airs and talk to fans. I watch what they’re saying to each other, what they like, what they dislike. It’s a wonderful giant focus group.”

The show tries to design episodes that encourage viewers to watch live, which advertisers prefer. “We have a lot of OMG moments, jump-off-the-couch moments,” King said. “It creates event television. That has sustained our place in the ratings as well.”

Andrew Lincoln as Rick Grimes and Norman Reedus as Daryl Dixon - The Walking Dead _ Season 5, Gallery - Photo Credit: Frank Ockenfels 3/AMC Our buds Andrew Lincoln and Norman Reedus in a pickle as usual. CREDIT: AMC

Credit: Rodney Ho

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Credit: Rodney Ho

“The Walking Dead” (AMC)

Season five starts Sunday, October 12 at 9 p.m.

What it is: A mix of character study and horror in a post-apocalyptic zombie world.

Average viewership: 18.4 million

Facebook likes: 30 million

Instagram posts: 1.5 million

Average tweets during an episode: 576,000

Why it works for social media: During any given episode, a major character could die. "We call it collective mourning," said Linda Schupack, executive vice president for marketing for AMC. And even when one doesn't, there are plenty of cool zombie kills to gape over with friends.

AMC works hard to keep fans engaged even during the offseason, including an extended trailer released in July that has been viewed 9.5 million times on YouTube. Last week, the network asked people what their final post-apocalypitc Tweet would be using the hashtag #finalpostFriday, which trended for three hours.

Three seasons down, how many more to go? If Twitter is a guide, it will be around awhile.

Credit: Rodney Ho

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Credit: Rodney Ho

“Love and Hip Hop Atlanta” (VH1)

Season three concluded Sept. 8

What it is: Atlanta hip-hop players tackle love, pettiness and occasionally, business.

Average viewership: 4.4 million

Facebook likes: 3.6 million

Tweets per episode: 800,000, the most popular show in America in terms of tweets

Why it works for social media: Jerry Springer-style battles pop up almost every episode, which garners plenty of frenzied, judgmental Tweets. Are scenes real or staged? Most fans don't seem to care.

Tom Chirico, VH1's vice president of digital and social engagement, said after doing some online focus groups, the network this past season shifted the tone of its official Twitter feed from a bland marketer to that of a nutty super fan with special access to the cast. They also held a "social media boot camp" for cast members to help them build their own fan bases. The show saw a 50 percent spike in Tweets per episode from season two.

The show also did post-mortem online show with popular “Love and Hip Hop” bloggers the morning after episodes aired. And during the reunion shows, producers highlighted popular video bits created by fans.