Who is online right now?
Who teaches you French?
"Who" serves as a singular subject so it takes a sigular verb; add -s or -es to the end of the verb.
Or simply use past tense, for example,
Who was there?
Who told you this?
How many memebers are online now?How can I make it plural to ask about more than one person?
There are 5 members online now.
Does that help?