Should Instructors Use Social Media to “Monitor” Students?

You all might hear this news: 

"18-year-old Robert Brever of Broken Arrow Oklahoma allegedly stabbed his parents and three siblings in a late-night attack. Authorities have charged him with five counts of first-degree murder and a count of aggravated assault."

Oklahoma police are searching Brever’s social media accounts, including Facebook and Pinterest, trying to find clues about his motives. This way to find more insight about criminal suspects is not new. Also, social media can provide police with warnings, because people nowadays are open to share their experience, interest, and thoughts in social media.

Drawn inspiration from police using social media, it seems like that instructors should use social media to get to know their students, their students' performance, opinions about the instructors and courses. For example, knowing students' interests could help instructors design and develop instruction material and strategies and thus motivate students.

On the contrary, there are still many challenges in implementing this in the real world. Doing this means that instructors should spend much more time after the class. Also, will students post their real thoughts when they know that their instructors are "monitoring" them. More importantly, students might not like to be known through their social media. Even if students friend with their instructors, they still could block instructors seeing some posts by changing setting in social media.