The prophet is reported to have said:
visits an 'Arraf (عَرّاف) and asks him
about anything, his prayers extending
to forty nights will not be accepted. (Sahih Muslim: 5540)
Going to an 'arraf (e.g., a diviner, seer or fortune-teller) to seek knowledge of the unseen is clearly against the sunnah of the prophet; it can also be considered a form of shirk, since the 'arraf are claiming to know what God alone knows as He said:
6:59: And with Him are the keys of the unseen; none knows them except Him...
And as for anyone who claims to have knowledge of the future, God said:
31:34: ...And no soul perceives what it will earn tomorrow, and no soul perceives in what land it will die...
So it seems clear that anyone who goes to an astrologer for the purposes of knowing and predicting the future has strayed from the straight path.
That said, I know of nothing against using astrology for purposes other than discerning the unseen. For example, there are many astrologers who claim, through (pseudo-)scientific observations made over generations, that the positions of the stars may influence your personality or behaviour; rather than trying to know the unseen, which is God's alone to know, they are trying to explain observable phenomena using other observable phenomena.
Although I know of no strong evidences forbidding such practices, or following those who espouse them, it is still probably better to avoid them since astrology in general is so strongly correllated to fortune-telling.