Matt Duffer previously said there would be "four newcomers" in the show's second season. A less certain factor is whether Eleven will be making a return, with Ross Duffer saying "we leave that up in the air." The second season takes place about a year after the first season ends.
Stranger Things got renewed for a second season on Netflix just yesterday, although there has been discussion of the show's return for a few weeks. Matt Porter is a freelance writer based in London. Make sure to visit what he thinks is the best website in the world, but is actually just his Twitter page.