Facebook (FB) is working on a chat room feature called Host Chat, TechCrunch reports. Users can restrict who's allowed to join a chat, and Facebook's news feed will be used to alert "friends" of an ongoing chat. The report comes as Facebook tries to maintain its messaging momentum amidst strong growth for WhatsApp and other mobile messaging rivals, who are often seen as threats to Facebook's mobile engagement rates. WhatsApp recently announced it now has 250M+ monthly active users. Messenger, which is baked into Facebook's core mobile apps, had 56.7M MAUs for its standalone apps as of last November.