They report on Twitter that Timothy Zahn was contacted in November, 2015 (source).

The Star Wars Actors Guild 77 started the Get Thrawn In Star Wars Rebels campaign in February, 2015 (source), simply due to bullying by “Star Wars fans” that doxed the owner of SWAG77 in this post .

All the hate by “Star Wars fans” to get Thrawn in to Star Wars have received about SWAG77 involvement needs to be revisited here: paypal.me/SWAG77/250

The image above was done in January 5, 2015.