Well technically the singular 2nd person thee and thou have stopped being used, so it's the singular that missing.
(Although you occasionally hear someone use thyself.)

or any plural term works, you do not need to qualify it by putting a you before hand. People, gentlemen, fartwits, etc.

Thank you for spelling "y'all" correctly. It's a contraction of "you all" with the apostrophe filling in for the 'ou' letters in "you". It gives me physical pain to see it spelled "ya'll".

1 Sheep, 2 Sheep, Black Sheep, Blue Sheep.

... I suspect the blue one/s was/were white before being left in the sheep-dip too long.

Sorry was this about people? ;p

As well as "you."

@AussiePengwin
Well, "you" isn't specifically a plural, is it?

@Hinoron
...Yes it is. In this context.

@Hinoron #9731452
It used to be. Plural oblique.
First person singular: I see him. He sees me. This is for me.
Second person singular: Thou seest him. He sees thee. This is for thee.
first person plural: We see him. He sees us. This is for us.
Second person plural: Ye see him. He sees you. This is for you.

What is happened in English is equivalent to dropping "I", "me" and "we", and using "us" instead in all cases.

@Klaus Basically, using the equivalente to the royal we for second person. Other languages did the same for a time, but they backtracked later... mostly.
An example would be spanish, which as a token of respect in polite language used plural "vos" (and the title, with plural posessive, "vues[tr]a merced") instead of singular "tú", but later returned to the "tú" (leaving for politeness the evolution "vuesarced>usarced>usted") in most places, except in a select number of Latin-American countries where the exact same phenomenon as in english happened (mainly Argentina).