Social media posts and comments provide a rich source of text data for academic research.
Refer to Searching social media - to get an overview and quick tips to get started.
The following journal article is written for researchers seeking to analyze social media. It presents a comprehensive review of software tools for social networking media, wikis, blogs, chat apps and news feeds.
Many social media sites have APIs (application programming interface) that provide access to textual content, including Twitter, Facebook, and YouTube. Using these APIs requires, generally, some technical know-how and an access key from the data provider.
Using tools built by others
LinkedIn - Social scientists working with LinkedIn data