I’m waiting for you to answer me on StackExchange.
Should I use waiting for you or waiting you? Why?
Use a Preposition
Waiting is an intransitive verb. That means it does not1 take a direct object. There is no thing directly affected by the verb, as it is implied that the doer (subject) of the waiting is the one who is affected. If you wish to indicate why the subject is waiting, you do so with a preposition - usually for but occasionally on (see below).
A: She is waiting. [note: We already know what party is affected by there verb - SHE is]
A: She is waiting for a friend to arrive. [The arrival of the friend tells us the circumstances under which the action was performed]
1 I can think of two exceptions: Wait tables, in which wait has a totally different meaning, and wait your turn which is a packaged phrase.
Waiting on is sometimes used in American English. It is more a regionalism than a socio-economic indicator. You don't hear it much in the Pacific Northwest, where I live, but in Texas and the Deep South it is more common.
Waiting on sounded good enough to the Grammy award voters who named John Mayer's Waiting on the World to Change the "Best Male Pop Vocal."
There is extended discussion of the regional nature of this over on English.se
My recommendation is that you use wait for. While waiting on is common in some regions, it sounds very weird to people who are not from those regions, whereas everyone is comfortable with wait for.