Formal:
* À jeudi! (Literally: "Until Thursday!")
* Je vous retrouve jeudi. (I'll see you on Thursday.)
Informal:
* On se voit jeudi. (We'll see each other on Thursday.)
* Jeudi alors! (Thursday then!)
* Je te retrouve jeudi. (I'll see you on Thursday.)
You can also use a more specific phrase, such as:
* On se voit jeudi après-midi. (See you Thursday afternoon.)
* À jeudi matin. (See you Thursday morning.)
The best way to say it depends on the relationship you have with the person you are talking to.