A bad attack of insolvency around 2011 left ANES with no choice but to shift its focus to more profitable routes in order to survive.
The Agios Nektarios has always run between Piraeus and Aegina, and still does. She's never even visited Symi.
The Proteus has been moved to the Sporades and seems successful running between Volos and Alonissos, Skiathos and Skopelos.
The Symi II remains in Mandraki Harbour, Rhodes but did get drydocked last summer so might reappear in service at some point.
Basically if you wanted to get to Symi in 2015 (or 14 or 13) it was a choice of Dodekanisos Seaways or Blue Star as the only two companies with licensed ferries on the route. Dodekanisos Seaways now have a largish passenger/vehicle ferry, the Panagia Skiadeni, which is dedicated to the Rhodes-Symi route, as well as the high speed catamarans you will probably remember.
They are supposed to be getting a third catamaran, but whether it will arrive this year I don't know.
You are not allowed to use the day excursion boats from Rhodes to travel to Symi except as a daytripper, so no single tickets or period returns, and no baggage. This is enforced by the Port Police/Coastguard who are much more visible than in the past at both ends of the route. This isn't a problem really as the Panagia Skiadeni runs at the same times as the day excursion boats, is faster, and much better fitted out.
Keep an eye out here and I'll produce summary ferry timetables once they are issued, or the Symi Visitor Travel Blog can be found at
http://symivisitor-accommodation.com/blog/and this includes flight information, and how to get from Rhodes Airport to whichever ferry you plan on using.