Here's the tweet that was sent:
En 2015 Pixar estrenará'Toy Story 4', se confirman las voces de Tom Hanks, Tim Allen y Joan Cusack en los personajes principales
— Jorge Luis Balaguera (@GeorgeBalaguera) February 18, 2013
I spent some time this morning and afternoon double and triple checking things, and I'm comfortable calling foul on this one, top to bottom. It's not happening. There's no story, there's no team at Pixar working on this, there's no energy being spent on the thought of a "Toy Story 4." Right now, Pixar is busy with a number of projects. There are "Toy Story" related efforts being made, but in the form of short films that we've been seeing for a while. On the feature side, they've got a very busy slate, with "Monsters University" set for this summer, "The Good Dinosaur" set for May of 2014, and "The Untitled Pixar Movie That Takes You Inside The Mind" set for June of 2015. On top of that, there's a Dia De Los Muertos film set for sometime in the future that Lee Unkrich is directing, and if they're doing a one-a-year schedule, then that's their 2016 release.So there you have it. No Toy Story 4 in the immediate future. But do we really even need a fourth? The third wrapped everything up nicely, in my opinion -- so a fourth is sort of pointless, really.
Source: HitFix