Some neighborhood-based social media can be useful, too, in emergencies.
In my corner of the world, many WhatsApp groups are based on neighborhoods or extended families. There is a group for my extended family in several countries, and we share news about weddings, funerals, or other family occasions. Also, neighborhoods may have whatsapp group to share info and congratulations or condolenses. Time to time they share info about house robberies or health info or whatever .
Due to my knee problem, I posted a question about the best physiotherapy center in town, and got some good info.