Just discovered this site and I am appalled

I'm a computer science teacher at a high school, and I was busy making the notes for my lesson tomorrow when one of my students, I'll refer to him as Jack (not his real name) came to me with concerns that his friends are bullying him on Twitter. Jack is an autistic senior and is very bright, though his social skills are lacking. For this reason, all of his friends (including these ones) pushed him to make a Twitter account so that he can be more connected to them outside of school. Jack recently made the acccount, posting updates about his day and the classes he goes to, and all his friends would talk to each other using the account as well. I told Jack that I would take a look at the tweets since he said the bullying had moved to Twitter, and he gave me his login information. I took a look at the tweets, and sure enough they were making fun of him for being autistic, his weight, etc, etc. But that's not the main issue; the main issue is that they've been posting links and sending him pictures from this site (4chan) making fun of his physical appearance. As I said, Jack isn't very socially aware, and he clicked on the links thinking his friends were sending him funny images. These images have the worst slurs and stereotypes that I've ever seen, and he told me these images and links were posted on his Twitter. The worst part is that I am worried these links may have been malicious, and I'm not sure if I should tell Jack's parents. How would you recommend I approach this?