The year in social media. Once again, katie couric. Reporter: If it happened in 2012, you probably saw it on social media. The events of the year weren't just taking place in front of you, they were... See More
The year in social media. Once again, katie couric. Reporter: If it happened in 2012, you probably saw it on social media. The events of the year weren't just taking place in front of you, they were taking place with you. Such an unusual storm, a yuns in a generation event. As a superstorm raged, you were sharing hundreds of first hand videos. Oh, my gosh. We do have breaking news tonight. Reporter: When a legend passed, you were posting Listen to the crowd out in times square. Reporter: And as a president was elected, you were tweeting over 300,000 tweets per minute. ♪ the site that started it all, facebook, had a lot to "like" in 2012. It reached one billion users. And a relationship status update, ceo, mark zuckerberg went from "in a relationship" to "married," with long-time girlfriend priscilla chan. Let's do this! Reporter: But it wasn't all good new on the time line. After much hype surrounding facebook's ipo, disappointment on wall street left people wondering, "what just happened?" After a day of trading, shares were only worth 23 cents more than they started. The person I feel worse for is zuckerberg 'cause he went from being a billionaire, to still a billionaire. That's gotta be rough. Reporter: If you watched any television show in 2012, you might have noticed something new. It's there right now. No, not a number sign. It's a hashtag. The little pound sign that started as a way to organize conversations on twitter, now a cultural sensation. People have started using hashtags almost as strange parentheses where they say what they're really thinking as opposed to what they just wrote. Reporter: The act that brought us the hash tag also let us see celebrities in a whole new way. It's a new phenomena, the celebrity who overshare on twitter. We don't know that you went to go pea and had a bagel at the same time. Celebrities who are using twitter, the people who hound celebrities shouldn't say that. They can't stop them from suddenly sending out a tweet in which they oops, attach a naked photo. Reporter: Alison pill accidentally sent this topless tweet while trying to delete it from her phone. Justin bieber was almost sued when he tweeted call me right now with this phone number. The last digit, a question mark. Frenzied fans dialed every combination of the number. Call me back, I love you! Bieber's fan never rang, but for these dallas residents, it's r stopped. I was getting three calls a second. As fast as I could hang up the phone, it would rering. Reporter: Hash tag, don't call me maybe. It wasn't just twitter and facebook monopolizing our time this year. The rising stars instagram and pinterest seemed to come out of nowhere. But the true break-out star of social media in 12, the meme. But what is it? A meme is an instant trend based on an image that often been manipulated. Reporter: When mitt romney threatened to cut off pbs during the first presidential debate. Sorry, jim, I'm going to stop the subsidy to pbs and I like big bird. Reporter: Thousands flocked to facebook, sharing, save big bird. Oh! Reporter: A member of the fab five, mla mar oni became a social media sensation after making this face on the medal stand. For a split second she was biting the side of her list and she looked unimpressed. Reporter: The moment was QUICKLY coined McKayla is not impressed. And so was the meme. To make that face, you basically have to look as disdainful as you possibly can. Mar oni took the look on her tour and everyone from david letterman to the president 0/20 r. There was one image that stood out from them all. Obama won by a lot. This photo of president obama and michelle obama is the most liked on facebook and the most retweeted of all time. It's infamous and small and showed a gesture between a husband and a wife. It was the first time that a president acknowledged he had won his election in 5i tweet. It's a sign to come of how leaders will try to communicate to their supporters using social media. Reporter: What's next for social media in 2013? You'll just have to follow to find out.
This transcript has been automatically generated and may not be 100% accurate.