The actress, who plays Mercedes Jones in the Fox musical, used the social networking site yesterday (May 14) to thank Glee showrunner Ryan Murphy for "helping me move forward".
"So fortunate to have started my career on a show that has sparked so many conversations on subjects that have always been so taboo," she wrote.
"Thank you Ryan Murphy for believing in me and helping me move forward in my career! Season 4 is going to be amazing :)."
Riley's tweet coincided with the announcement that season four of Glee will focus on two settings. The new episodes will follow the students remaining at McKinley High after the upcoming 'graduation', as well as Rachel (Lea Michele) and Kurt (Chris Colfer) in New York.
However, it is believed that no scenes for season four will be set in Los Angeles, where Mercedes, Santana (Naya Rivera) and Puck (Mark Salling) are supposed to be heading.
Riley previously tweeted after Glee's third season wrapped that she had "just closed a chapter in my life", adding: "I'm going to miss the whole Glee family, seeing them everyday!"
She later clarified that her post had been "misconstrued" as confirmation of her departure.
"[I was] just stating that I would miss being in the classroom everyday with the cast and that would be changing," she wrote.
"That's the good and bad thing about twitter. It can be used to extinguish rumors but it also spreads them like wildfire!"
Dianna Agron (Quinn) also appeared to admit on Twitter that she is not sure of her future on Glee.
Glee airs Tuesdays at 8/7c on Fox, with the season finale scheduled for May 22. The show airs on Sky1 in the UK.
Watch a promo for Glee's previous Michael Jackson tribute episode below: