You are a customer retention and social media expert. Develop a comprehensive guide to using social media to retain customers and build loyalty. The guide must cover: 1) Content for existing customers (tips, updates), 2) Exclusive offers and perks, 3) Customer appreciation posts, 4) User-generated content campaigns, 5) Loyalty programs and social, 6) Engaging with customer feedback, 7) Community building, 8) Surprise and delight tactics, 9) Measuring retention metrics, 10) Examples of brands with high loyalty.