Mark Ruffalo, who is playing the Incredible Hulk in Joss Whedon’s The Avengers: Age of Ultron, tweeted several photos from the first day of shooting including a selfie-like "Science Bros." shot with co-star Robert Downey, Jr., and a photo of Scarlett Johansson from behind with the caption "Almost got her!!!." 

Joss Whedon’s Avengers: The Age of Ultron is slated to debut nationwide on May 1, 2015.
 
The rise of social media has allowed stars and directors to begin to publicize their films during the production process, and an increasing number of both behind-the-camera and on-screen talent have availed themselves of the opportunity to raise awareness of their film projects.  Will this temporally-advanced publicity continue to be utilized?  Since the cost is negligible, the answer is obviously yes, at least until the novelty wears off. 
 
Before the rise of social media, other production elements such as concept art were often kept under wraps and not revealed until the publication of a “making of” book, but the rise of Internet has encouraged producers to release cool concept art to whet the appetite of fans even before the movie is in production (see "'Avengers: Age of Ultron' Concept Art for Scarlet Witch, Quicksilver").
 
Not to be left out, Robert Downey, Jr. tweeted a photo of himself with executive producer Jeremy Latcham.