LinkedIn. The website may sound to you like a place for consultants and other folks in the industry. You may consider ResearchGate and your blog as your online venues of choice. Perhaps you prefer to interact on Twitter. Maybe you once made a profile on LinkedIn when you were an undergraduate student, and then never updated it. Wherever you are, I'd recommend you to build and maintain a profile on LinkedIn. For academics, LinkedIn can serve the following purposes:
Sometimes, your profile page on your institution or your blog can become more difficult to find. Your LinkedIn profile can be a good tool to monitor and manage your personal online brand. It can be a source of consistency as you switch institutions. Use it to have your most important information and specialty online, and keep it updated.
Your summary on LinkedIn is your online elevator pitch. Use a paragraph to summarize where you studied and worked in the past, your current position, and your service appointments if these are important in your field. Keep this summary updated in the same way you keep the summary of your resume updated. Whenever you are invited somewhere as a speaker, you can simply copy and paste this summary for your introduction.
E-mail addresses are unreliable, especially for early career researchers. If you move from short-term post-doc project at one institution to another place, it can be difficult to keep in touch with your contacts. I use LinkedIn as my digital address book - and one that updates itself all the time. The only drawback of this approach is that it may be harder to get a response from a colleague when he/she has a profile, but actually doesn't use LinkedIn at all. Whenever I receive a business card, I search for the name in LinkedIn, and add this person as a contact - business cards get lost easily, but a LinkedIn profile connection can stay (provided that a contact doesn't block you or deletes his/her profile). An added plus is that you will get notified when a contact has a birthday, changes jobs, or has a job anniversary. These occasions are always good to touch base.
Consider LinkedIn your online CV. Update it regularly, and add the information that you have on your CV: educational background, work experience, honors and awards, language proficiency, skills and publications. Moreover, you can link LinkedIn to other services such as Slideshare to showcase your presentations, and to Publons to have your verified peer review record visible. If your graduation is approaching, make sure your LinkedIn profile is up to date, does not have spelling errors, and gives a good overview of your contributions to the profession.
Just as with other social media, you can join groups on LinkedIn, and participate in these groups. You can ask questions, and/or answer questions. If you are getting towards graduation and consider a job in the industry, interaction in professional groups can be an excellent way of getting noticed.
You can follow business pages on LinkedIn (institutions and companies) to keep up-to-date with some important players in your field. These pages can notify you of open positions, and give you a general idea of the culture of a certain institution beyond what is available on their webpage. The same holds true for other social media platforms, which are all less static in nature than a website.