There needs to be a button with the words "Get Help" on it. When people click on it the leviathan banner will be on the top of every players' screens. The leviathan will show up on the main map and can be warped to.
There should also be a setting to turn this off in settings under the name of "Disable the leviathan banners of other players" when clicked
it will not display the banners for other players' leviathans.