The concepts behind "social networking" aren't anything new - ever since there have been humans, we have been looking for ways to connect, network, and promote with one another - but they've taken on an entirely new meaning (and momentum) in the digital age. Where we used to have handshakes, word-of-mouth referrals, and stamped letters, today's relationships are often begun and developed on LinkedIn, Google +, and Facebook.

That means savvy business owners have to know and use a variety of social platforms to stay relevant, not to mention take advantage of emerging opportunities. Below, you'll find what I consider to be the 21 most important channels and tools you need to be aware of.

1. Twitter. Perhaps the simplest of all social media platforms, Twitter also just happens to be one of the most fun and interesting. Messages are limited to 140 characters or less, but that's more than enough to post a link, share an image, or even trade thoughts with your favorite celebrity or influencer. Twitter's interface is easy to learn and use, and setting up a new profile only takes minutes.

2. Facebook. Considered to be synonymous with "social media" by some, Facebook is the one site where you're likely to find friends, colleagues, and relatives all floating around. Although Facebook is mainly centered around sharing photos, links, and quick thoughts of a personal nature, individuals can also show their support to brands or organizations by becoming fans.

3. LinkedIn. One of the only mainstream social media sites that's actually geared towards business, LinkedIn is to cyberspace what networking groups once were to local business communities. It's great for meeting customers, getting in touch with vendors, recruiting new employees, and keeping up with the latest in business or industry news. If it matters to your company or career, you can probably do it on LinkedIn.

4. Xing. Another professional networking and recruitment site, Xing has the global presence and focus that LinkedIn lacks. Although it can be mistaken for a job search portal, the site actually has a number of features and communities that make it easy to develop relationships with suppliers, colleagues and even thought leaders within industry.

5. Renren. Literally translating into "everyone's website," Renren is China's largest social platform. Hugely popular with the younger crowd, it works in a way similar to Facebook, allowing users to share quick thoughts, update their moods, connect with others, and add posts or ideas to a blog-like stream.

6. Google+. Social media's big up-and-comer has really arrived over the past few years. By combining the best of Facebook and Twitter into one site - and backing it by the power of the world's largest search engine, Google has given users a social site that has a little something for everyone. You can add new content, highlight topics with hashtags, and even separate contacts into circles. And, a G+ profile only takes a few minutes to get set up.

7. Disqus. Disqus isn't actually a social media platform so much as a social engagement platform, but it can definitely help you improve your social engagement. As a tool for commenting, managing feedback on your own website (or other Disqus-enabled websites), and managing spam/troll type messages, it's invaluable. Advanced features allow for social monitoring and upvoting.

8. LinkedIn Pulse. Even though Pulse is technically a part of LinkedIn, it's big and important enough to deserve its own entry. Serving as something between a blog and "best of" outlet, it's the perfect medium sharing new ideas and keeping up on the thought leaders in your industry.

9. Snapchat. This surprisingly-addictive app gives you the ability to take a picture, add art and text if you'd like, and then send it to recipients for a set amount of time (after which the photo will delete itself and be removed from the company's servers). Lots of fun, and potentially a good way to stay in touch with friends.

10. Tumblr. This platform is different form many others in that it essentially hosts microblogs for its users. Individuals and companies, in turn, can fill their blogs with multimedia (like images and short video clips). The fast-paced nature of Tumblr makes it ideal for memes, GIF's, and other forms of fun or viral content.

11. Pinterest. Serving as a giant virtual idea and inspiration board, Pinterest has made a huge impact on social media in the last few years. Especially popular with women and the do-it-yourself crowd, it lets you share pictures, creative thoughts, or (especially) before-and-after pictures of projects that others can pin, save, or duplicate.

12. Twoo. This Belgian social network site is geared for the 25 and under crowd all over the world. Alongside normal social features like posts, updates, and photo sharing, it also boasts online games and chat features that make it popular with younger users who want to stay entertained while connecting with each other.

13. MyMFB. Created as a Muslim alternative to Facebook (it was previously called MillatFacebook), this site aims to connect the faith's 1.5+ billion followers into a single social platform. While that might sound ambitious, it's growing quickly and offers many of the same post, update, and sharing features as the original Facebook, and is already immensely popular in some parts of the world.

14. YouTube. As a video sharing service, YouTube has become so popular that its catalog of billions and billions of videos has become known as "the world's second-largest search engine" in some circles. The site has everything from first-person product reviews to promotional clips and "how-two" instruction on virtually any topic or discipline. Users have the ability to share, rate, and comment on what they see.

15. Instagram. If you're looking for a quick, convenient connection between the camera feature on your smart phone and all your social profiles, then Instagram is the answer. Not only will allow you to share via Twitter, Facebook, and the Instagram website, you can choose from a variety of photo filters and invite friends to comment on your photos or ideas.

16. Vine. This site (also available as an app) offers users the chance to share and view brief video clips. While that theoretically offers a virtually endless range of uses, most of Vine's content is entertainment-focused, with a heavy preference towards "viral" and "meme" clips that are easy to share.

17. WhatsApp. The WhatsApp concept is simple: send text-style messages to anyone else using the platform, but without paying data charges. That straightforward idea has already gathered more than 700 million fans, making the app the world's most popular messaging platform.

18. vk.com. Promoting itself as Europe's largest social media site, vk.com is essentially the Russian version of Facebook, with the same kinds of profiles, messaging, and games you would expect. Like Facebook, vk.com allows users to enter both personal and professional information about themselves, and to follow or show support for organizations and businesses.

19. Meetup. Meetup is a perfectly-named platform, because it's perfect for organizing local groups around specific interests. There are meetups centered on just about everything, from music to hobbies, and get-togethers are almost always open to newcomers. That makes it perfect for exploring an interest and making new friends at the same time.

20. Secret. This might be the best social media app most people haven't tried. The premise is simple: join into a group of friends (or create your own), and then share an anonymous message. It's great for fun interactions, idea starters, or just finally getting something off your chest. (Editor's note, 5/13/2015: Secret has folded. Co-founder David Byttow writes: "After a lot of thought and consultation with our board, I've decided to shut down Secret. Over time, I plan to publish postmortems so that others can learn from the unique mistakes and challenges we faced and the wisdom gained from such an incredible 16 months.")

21. Medium. If you've ever wished that social engagement could come with an ongoing, up-to-date "how to" manual written by the experts, Medium might be just what you're looking for. With lots of helpful advice, tips, and articles, it can give you everything you need to start connecting like a pro.

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