While Blog Posts often can appear on websites of reputable organizations or schools, it's also important to remember that Blogs can be written by anyone. They are usually considered more informal and do not go through any type of review process like scholarly articles are, no matter where they are posted.
This does not mean that Blog posts can't be used as sources in your papers, but it is vital to fact-check, look into the author, and look into the organization that is posting the blog. Blogs are notorious for being more biased and, very often, are opinion pieces. Blogs are also often sponsored. Make sure that whoever is sponsoring the Blog you are looking at isn't someone who has an agenda with the topic. For example, you would never want to take advice on a Chevrolet truck on a blog that is sponsored by Ford.
Social Media, in various forms, dominates society today. Occasionally, you may find a post of various Social Media sites that you would like to include in your paper. It's one way to access either the subject or the authors first-hand views on a subject, among other things. Not all instructors will allow you to use Social Media posts. Make sure that with the ones that do, it is not the only source that you rely on. Social Media will not have the depth needed for a college level paper.
Social Media is not fact-checked in any official capacity, so make sure that you are verifying that the information in whatever post you are using is accurate. Anyone can say anything of Facebook or Twitter and images are altered all the time using Photoshop technology. Do not take anything at face value, especially if using it for a paper.