I am on 100 mg of Zoloft currently, though I wouldn't say I have been on it that long. I, as of now, have not noticed a change in my weight either. I did with Lexapro (gained). Meds work differently with everyone, so you'll have to see if it works for you. Weight gain is a concern of mine as well, so I steer clear of ones that might do that either.
I used to take Zoloft many years ago. I took it for 4 full years at 150Mgs a day and it had absolutly no effect on my weight.
Paxil on the other hand is one SSRI that seems to add pounds. Tri-cyclics and Tetra-cyclics absolutly do cause massive weight gain with no doubt.
Meds like Prozac, Effexor, Welbutrin and Cymbalta never had any impact on my weight either.
I do know that Paxil, Nortriptilyne, and Remeron are very much associated with massive weight gain in most people. (may want to stay clear of them if weight is an issue.)