Keep in mind, we're not just talking about accounts used by actual terrorists to coordinate actual attacks. We're talking about "pro-ISIS" Twitter accounts.
How will we decide who is pro-ISIS? I propose a system of hearings, with the most important ones conducted by a senate committee. The most important question at these hearings will be "are you now or have ever been a sympathizer with Islamic State." If they "fail" the hearing we could put them in some kind of database used by employers and government hiring agents and so forth. A sort of blacklist, if you will.
And anyone on the blacklist doesn't get to use corporate media platforms. It's not a First Amendment violation, you see, because it's VOLUNTARY. Just ask these guys: https://en.wikipedia.org/wiki/Hollywood_blacklist