http://www.ssbwiki.com/Smasher:T0mmy used to be a pichu main. I don't know if he is still active, or if there are any active mains though.
T0mmy is looooong retired.
He was also never that notable as far as tournament results went...
He did do a lot for the pichu meta back in the day, but he's no Taj.
As far as Pichu players go, there have never really been any that were getting super notable results or could preform with him at a high-mid level the way players like RRR have with kirby or Cosmo! with Zelda or other examples along those lines.
While I will never say that a character doesn't have potential to develop, and that incredible players can't see success with a character like pichu, I will say that it is very unlikely that we will see anything like that at anytime soon (although I seriously hope that we do).
As far as active pichus right now I think ICG might be the only one... and as much as I love the kid he's not getting results either.
there have been some that popped up every now and again that were lookin pretty legit (i.e. Tuna Salad, Unknown522 back in the day) but they either didn't stick with the game or switched to characters that suited them better for tournament success.
Doesn't mean it's not doable, just that it's really really difficult and hasn't been done yet.