fakester
n. A person who puts up a profile on a social networking website such as Friendster or MySpace that contains false or misleading information, or that is dedicated to another person or to an object.
Examples
2006
In the early days at Friendster, only real individuals could create profiles. Bands were lumped in with other "fakesters" the term coined by Friendster users for profiles created by impostors or dedicated to someone other than the author, such as a pet or a celebrity. The company eventually relented, and fakester profiles became an accepted part of Friendster's culture, often taking on the function of fan clubs.

MySpace, however, has been hospitable to fakesters from the beginning—so much so that it's now perfectly kosher for a company (or one of its fans) to create a profile for a fast-food chain, a brand of soda, or an electronics product.
—Wade Roush, “Fakesters: on MySpace, you can be friends with Burger King. This is social networking?,” Technology Review, November 01, 2006
2006
"Freaks, geeks and queers all invaded Friendster in the early days and they made certain that all of their friends were there," Boyd wrote this year on her blog. As more communities joined, Boyd noticed new and unexpected behaviour. … Some users — known as "fakesters" — registered under pseudonyms such as Ali G, LSD or Homer Simpson. …

In contrast to Friendster, MySpace encouraged people to put up wacky art or even pipe music on to their pages. Music, and the culture around it, became an important part of the site. Most fakesters and other group characters were allowed.
—Graham Bowley, “The high priestess of internet friendship,” The Financial Times, October 28, 2006
2003 (earliest)
Batty and numerous other Friendsters routinely violate the site's user agreement by creating fictional characters as profiles instead of, or in addition to, their "real" profiles. These "fakesters" portray themselves as everything from inanimate objects like the World Trade Center to celebrities like Paris Hilton to historical forces like War (which lists its profession as "resolving disputes"). …

But fakesters aren't hosting this gig. Jonathan Abrams, the 33-year-old software engineer who founded Friendster to improve his own social life, is — and he abhors the phony profiles. He believes they diminish his site's worth as a networking tool and claims that fakesters' pictures — often images ripped off the Web — violate trademark law. Abrams' 10-person Sunnyvale company has begun ruthlessly deleting fakesters and plans to eventually eradicate them completely from the site.
—Lessley Anderson, “Attack of the Smartasses,” SF Weekly, August 13, 2003
Notes
And congrats to KROQ-FM deejay the Poorman, who nabbed a fakester passing himself off as comic-pitchman Joe Piscopo. Tipped off by the real Joe's agent, Poorman had the fakester on his show the other night. After the fakester discussed his latest career moves, Poorman produced the real Joe (on the phone from New York), his attorney (and a hidden "Hard Copy" crew, which was filming the proceedings).
—Patrick Goldstein, “Pop eye,” Los Angeles Times, October 07, 1990