The social news group BuzzFeed unveiled a major new expansion plan, using a fresh infusion of $50 million in venture capital. Andreessen Horowitz, the big Silicon Valley venture group, announced late Sunday it is investing $50 million in BuzzFeed and that one of its partners, Chris Dixon, will be joining the company’s board. Its video division will expand and become BuzzFeed Motion Pictures, which will focus on all moving images from a GIF to feature film and everything in between, according to a statement Monday.