I haven't seen or heard about anyone using snapchat in the last year. It used to be the location for all my family's chat. They definitely aren't experiencing explosive growth anymore.
Besides that, they've built out their first-party content platform pretty well, which I assume is what's driving their advertising growth, and (anecdotally) is shared in-app relatively frequently, although I've recognized some reposting/reformatting of said video content from Youtube or other sources, e.g. WatchMojo.