John Baez (https://plus.google.com/117663015413546257905/posts) (especially), Artem Kaznatcheev (https://plus.google.com/101780559173703781847/posts), Timothy Govers (https://plus.google.com/+TimothyGowers0/posts), Michael Nielsen (https://plus.google.com/+MichaelNielsen/posts) among others (but it's not a well-curated list; and I tend to use G+ less and less often, for too much noise).