5 Twitter stars you've never heard of

(CNN) -- Sure, everyone knows that Oprah, Shaq and Ashton Kutcher are huge on Twitter. They're famous -- they should be huge on Twitter.
But Heather Armstrong? John Dickerson? Adventure Girl? These people can stroll unmolested through a paparazzi convention, and yet each has more than 1.2 million Twitter followers -- enough to rank them in the top 200 overall and more than Stephen Colbert, Snoop Dogg or Paris Hilton.
To thrive on the popular micro-blogging site, celebrity isn't always enough. You also must have something to say.
"You can't be Moses shouting down the mountain on Twitter," says Brandon Mendelson, a blogger who has amassed almost a million Twitter followers. "You need to be that friend everyone wants to hang out with."
Here's a look at five Twitterers you may not have heard of. They don't show up in the tabloids or on Leno. But they have the power, through the viral effect of their retweets, to make things happen, and maybe even nudge the national conversation a little.