If your business is B2B, you should be active on Facebook and LinkedIn. Facebook is still the largest social media platform with over 2 billion monthly active users and has an outstanding ad platform that ensures your content is seen by the right audience. And LinkedIn is the official social media channel for the workplace.
If your business is B2C, however, you should be active on social platforms like Instagram, Pinterest, Snapchat, and Twitter. Look into what your audience uses and engage with them there.
P.S. remember the purpose of the platform—be entertaining and informative, not salesy.