The syntax help for the /particle command shows still:
/particle <name> <x> <y> <z> <xd> <yd> <zd> <speed> [count] [mode]
However (also based on Grum's comment) the syntax now looks like this:
/particle <name> <x> <y> <z> <xd> <yd> <zd> <speed> [count] [mode] [player] [params]