I wouldn't recomend Effexor for someone that is suffering only Anxiety dissorder without moderate to severe depression, but Effexor while primarily for depression also helps a lot for people that have generalized anxiety with depression.
I took Effexor for 4 years before it stopped working for me, but during those for years it did a very good job of controling my Depression as well as my Anxiety and panic attacks.
So for me it worked when other meds like Zoloft stopped working. Of corse that doesn't mean it will work the same for you.
my doctor put me on effexor for mild anxiety