Let’s say we invent a name like…“CeAsia”, then start posting about this fictional person and their antics on various websites. How far could we possibly get before the bubble bursts?
We might need to take fake pictures. I think few people who get invested with celebrities would get interested before they’ve seen pics.
Of course, I’m old enough to remember the Allegra Coleman Esquire Magazine hoax. 
It would be interesting to try; I’d give it a swing. But if you really want to do it, of course you can no longer use the name “CeAsia” (which is cacophonous, anyway) and need to have the discussion with a limited number of person via a non-Googlable medium.
They did that (or something like it) in 2011, with Aimi Eguchi, ostensibly then a new member of the group AKB48 who turned out to be a CGI creation.
And of course, Lady Gaga is actually a test-bed for Disney’s next-gen animatronics.
James Tiptree, Jr. wrote a short story based in part on this premise, called “The Girl who was Plugged In”. It’s a future world where advertising has been officially banned… so the advertising companies manufacture celebrities from whole cloth, who can then just happen to be seen using particular products. The main character, Philadelphia (re-named “Delphi”), is such a celebrity, and ends up engaged to some minor European prince before things start falling apart.
Of course-That’s why I said like “CeAsia”. “Ce Lo Phane” is out, too. 
Try CeA$ia
Milli Vanilli was a pop duo of singers hired for their looks and ability to dance. Turns out that their albums were sung by others. It did not end well.
…
They didn’t bother to invent a backstory for Hatsune Miku; everyone knows she is CG and no one cares (or that’s part of the attraction).
ETA: In case someone doesn’t think Hatsune Miku is a bona fide pop star:
There was also the horrid movie S1m0ne, which was at least tangential to your idea.
You could call him Captain Tuttle.
And my wife paid to see them in concert.
Aimi Eiguchi and Hatsune Miku were predated as virtual idols by Date Kyoko.
I’ve seen an interesting documentary about a similar concept being tried in the early 70s…
George Plimpton (writing for Sports Illustrated) did it as an April Fool’s joke in the 1980s. He created a guy named Sid Finch (IIRC), a Mets pitching prospect who could throw 160-mph fastballs. Lots of people got fooled.
Not to mention her hugely successful live concerts in Japan, Singapore, Hong Kong and Los Angeles, her international endorsement deals (including Toyota) and the thousands of songs and videos on YouTube and NicoNico.
For the unwashed, this 60 second spot sums up who and what she is:
You know that was only 1996 right? A long time ago, sure, but not something so ancient that the majority of this board wouldn’t remember it.
And how much of a hoax can it be when the model, Ali Larter, actually became a real actress a year later and who still acts in moderately high profile projects today.