The plaintiff generally gets to choose jurisdiction online. They only have to come up with a justification for any of the parties involved, even the owners of the website, which the judge in that country will accept, and they can settle it in that court. This is an extremely common practice in online cases which favors the accuser over the accused.
In this case the options would likely be the country @moonflower resides in, the country @r4fken resides in, or the countries the operators of SteemIt.com reside in.
necessarily or probably? As I understand it, unless you differ arbitration beforehand with other contracts such as citizenship, the accused has to consent first.