"No, I wasn't looking for you."
Translation:Ne, tebe jsem nehledal.
I answered 'Ne, jsem nehledal tebe' which was judged incorrect because I omitted 'ja' (sorry I do not have a Czech keyboard) before 'jsem'. Is 'ja' necessary when the sentence is worded that way?
Yes, it is. "jsem" is a clitic and it should be in the second position. At least in the standard language.