But despite the reach of Doppelganger Week, its origin appears to be a mystery.
In a piece for the Huffington Post, Alex Grossman transcribed an "Interview With Bob Patel, Creator of 'Doppelganger Week' on Facebook."
"It all started when the guys at work started teasing me that I look like Tom Selleck," "Patel" said. "They're like, 'Hey, Tom Selleck, what are you doing?' Or, 'Yo, Tom Selleck, we're talking to you.'"
But later in the comments section, Grossman sarcastically reveals Patel's true nature.
"More than a few people have questioned whether this interview and Bob Patel are real," he wrote. "Bob Patel is absolutely real. He lives across the street from Santa Claus, just around the corner from The Easter Bunny. Geez..."
In an e-mail, a Facebook spokeswoman said the site doesn't have the ability to track the origin or spread of trends like the Doppelganger pictures.
"Anecdotally, these types of things seem to start with one person or group of people ... and then spread rapidly through the social graph because of products like News Feed," she said. "By the time we recognize the trend, it's usually difficult to pinpoint the exact beginning."
And though many have joined the fun, some are already taking part in the protest.
The "Thanks to Doppelganger Week I Recognize Narcissists Right Away" group counts more than 200 people among its members.
And Kristy Korcz, associate editor of the blog GeekSugar, said that when her site asked users if they took part in the latest Facebook "theme weeks," most said "no."
She said this one seems particularly popular because so many people are caught up in celebrity gossip, especially during awards season, but the people who are participating in Doppelganger Week appear to be those Facebook users prone to status updates and frequent postings.
"The majority of users are saying I don't participate," she said about her blog's readers. "They use it to keep in touch with friends and family and don't want to play games."
Some, she said, are so done with the constant march of Facebook trends that they want them to stop.
But amusement or annoyance, Justin Smith, editor of the blog Inside Facebook, said the Doppelganger trend and other similar fads are likely here to stay.
"In many ways, what we're seeing is that some of these Facebook phenomena are replacing the old chain letters that our parents used to send," he said, adding that the social, connected nature of Facebook makes it easier than ever for information and applications to spread virally.
As more people join the site, he said he predicts the trend will only continue.
"I would expect to see more of these things," he said. "More fads spreading quickly."