Wasn't momo an issue a few months ago with rumored Self Delete attempts relating to it.
But to answer your question momo is some contact you'd add onto WhatsApp and it would start telling you dares, send you disturbing stuff, and would sometimes just harass you. Apparently it would find your info on other websites, but this kind of makes it seem like a bot since it can just search media sites like Facebook where you've put in your number. It also has to do with some disturbing videos or something, idk.