ive sold 8 cars trough autotrader.
put one on ebay, and didn't get close to what i wanted, reserve nowhere close to met.
i did get my car trough ebay, contacted the seller before aucion ended, made him offer, checked it out, bargained some more, and dropped the price even more, and i did get 3 trough craigslist.
best bet is autotrader.com cars.com craigslist.org and put it all over the Porsche forums, like here, 6speedonline, renntech, rennlist, make a cardomain page and state that its for sale.
also, go to carmax, they will completely examine your car and make you an offer, and if you don't like it at least you will have a printout of all the stuff that was looked at that can be a good asset when potential buyers ask whats wrong with it.
i had 9 cars so far, and i only broke even with one, all the other ones i made money on, and i now that with this one ill make money as well, couse i got it for way too cheap haha, its definitely a buyers market man, although i am enjoying this car too much to even think about selling it
good luck with the sale tho