Members of the group decided to set up their own version of Facebook, called Khelafabook, so they could chat with one another.
The name Khilafah means caliphate in Arabic.
Its home page features a world map in black and a tone of blue similar to that used by Facebook, complete with ISIS logos.
It is believed to have been built using a platform called SocialKit, which people can use to make their own personal social networks.
The site was established by a man in the Iraqi city of Mosul.
Its privacy policy page was blank and the site did not appear to have attracted many users.
But Khelafabook already appeared to have been shut down today, with a message posted on the webpage.
It said there had been a "temporary shut down" in order to "protect" the details of its users.