"Who are you going to meet up with tonight?"
Translation:¿Con quién vas a encontrarte esta noche?
I put "¿Con quién te vas a encontrar esta noche?" It was marked incorrect. Is that a correct placement of the pronoun?
Encontrar and encontrarse are different verbs. http://www.wordreference.com/es/en/translation.asp?spen=encontrar
I used encontrar, after checking various websites. The link you give translates both Spanish verbs as meet.
We don't, but if you use the formal "you," you have to make sure the pronoun matches.
And if you think the sentence is grammatically correct, but it is rejected, report it.
My question also. Doesn't using " vas" indicate it is 2nd person singular, so the " tu or te" is superfluous? Grammar scholars care to comment?
Using the different forms of "se" shifts the meaning of the verb. Sometimes it makes the verb reflexive, sometimes it makes it passive, and sometimes (as in this case) it just shifts the meaning. See elizadeux's comment above.