Will Darth Vader find Asokah

Answer 1

No she is not in Episode 3 which was right before Vader turned to the Dark Side, unless Ahsoka was alive during Episode 3, but just never shown.

Here's the way I see it:

Ahsoka was not around at all in Revenge of the Sith. Therefore, she either completed her padawan training (Extremely unlikely, considering that she had only been one for three years maximum), or she died somewhere between Attack of the Clones and Revenge of the Sith, thus making it impossible for her to have had any contact with Vader. Personally, I prefer the second option.