Welcome to Cruise Mates. Our last Carnival cruise had nightly singles meet and greet events. I don't think they were particularly organized. You can also search the web for organized singles cruises. This can be part of a regular cruise.
All I ask is a tall ship and a star to steer her by; John Masefield
Carnival: Glory 2004, Destiny 2008, Splendor 2009, Freedom 2011, Valor 2012, Dream 2013
Celebrity: Summit 2011
Princess: Ruby 2010, 2014, Caribbean 2013, Coral 2014, Regal 2014
Star Clippers: Royal Clipper 2015