Social media apps have become an integral part of modern communication and connectivity. They allow users to share content, connect with friends and family, follow their interests, and stay updated on news and trends. Here are some popular social media apps as of my last update in September 2021:

1. Facebook: The largest social media platform in the world, allowing users to connect with friends, share photos and videos, and join groups and events.
2. Instagram: A photo and video-sharing platform known for its visually appealing content and features like Stories and IGTV.
3. Twitter: A microblogging platform where users can share short text updates (tweets), follow others, and engage in real-time conversations.
4. LinkedIn: A professional networking platform for job seekers, professionals, and businesses to connect and share career-related content.
5. Pinterest: A visual discovery and bookmarking platform where users can discover and save ideas on various topics through pins.
6. Snapchat: A multimedia messaging app known for its disappearing messages (Snaps), Stories, and augmented reality (AR) filters.
7. TikTok: A short-form video platform where users can create and share creative videos set to music, often featuring trends and challenges.
8. WhatsApp: A messaging app for sending text, voice messages, and making voice and video calls, with end-to-end encryption for privacy.
9. Reddit: A platform where users can engage in discussions on various topics through forums called “subreddits.”
10. YouTube: A video-sharing platform for uploading, watching, and sharing videos on a wide range of topics and interests.
11. Tumblr: A microblogging platform that combines text, images, and multimedia content in short blog posts.
12. Discord: A communication platform primarily for gamers, but also used for communities and group discussions on various topics.
13. Telegram: A messaging app known for its privacy features, group chats, and channels for sharing content.
14. WeChat: A popular messaging app in China that offers a wide range of features, including payments, social networking, and more.
15. Viber: A messaging and calling app with features like group chats and video calls.
16. Clubhouse: An audio-based social networking app where users can participate in live discussions and conversations on various topics.
17. Mastodon: A decentralized social media platform that allows users to host their own servers and communities.
18. MeWe: A privacy-focused social network that promotes user data ownership and control.
19. Ello: A platform focused on artists and creators, offering an ad-free and privacy-focused experience.

Marketing efforts can also take advantage of the peer effects in social media. Consumers tend to treat content on social media differently from traditional advertising (such as print ads), but these messages may be part of an interactive marketing strategy involving modeling, reinforcement, and social interaction mechanisms. This study indicated that social media communication between peers about a product had a positive relationship with product engagement.