While it appears to be partially operational, Apple has yet to officially announce the Turkish Online Store, the webpage can be accessed via the usual "store.apple.com" address with an appended "tr" country designation.
As noted by Turkish Apple blog Shirli Elma, Apple's online store for the region is currently being updated and an advertisement has yet to hit the site's landing page. When users click on the "Store" option from the main website, they are sometimes taken to a page describing ways to buy Apple products, including official third-party resellers.
As of this writing, it seems that Apple is allowing order for at least some items, like the iPhone and MacBook Pro. The Apple Online Store is expected to officially go live in the near future as the a link is already provided on Apple's country selector webpage.