There's a talk one of the engineers gives[1] (that someone else posted here so I'm watching it) about their architecture that's published in March of 2014, and in it he talks about ~550 servers, which includes 250 multimedia servers and 150 chat servers.

The only places he mentions 16 is when he talks about the "multimedia database". I think there were 16 sharded database servers.

1: https://www.youtube.com/watch?v=c12cYAUTXXs