CartoDB ran an audio ad in the Data Stories podcast. One of the hosts read the text and pointed listeners to the company's gallery page. "Learn how CartoDB is shaping the world of location intelligence at cartodb.com/gallery." The topic of the podcast, ironically, is turning data, gravitational waves, into audio, rather than anything visual. I didn't listen to the podcast since I'd heard about the concept some time ago on NPR.
Mapbox is running a series of "ask me a question" posts on Reddit/GIS. These are not "Ask me anythings (AMAs) exactly, but an offer by Blake Thompson, a software engineer at Mapbox, to answer questions about specific GIS topics. First up were: algorithms and Web map APIs. As you can see, there was a good amount of interaction/engagement.