As a resident of Turkey, I can give the answer according to my own
experience in online shopping. There aren't many big retailers in
Turkey, so top 5 is not hard to extract:
http://www.Hepsiburada.com (formerly infoshop.com.tr)
The leading retailer of many kinds of goods. They carry a large
inventory, and they are backed by a leading media group (Dogan Group -
also the owners of a leading ISP, e-kolay.net).
Kangurum is actually a mall, a collection of many online shops in one
interface. This includes both food and non-food goods. The site was
mainly built for an online face for one of the country's leading
supermarket chains, Migros, and expanded to include many other shops
Leading retailer of culture goods (books, music and video) and many
other things. They started selling books only (a-la Amazon.com) and
expanded their inventory later. They are synonymous to online book
purchasing in Turkey.
Relatively new retailer of general goods, with a special stress in
electronics. They are backed by one of the country's biggest groups,
Uzan Holding (also the owners of the GSM service provider Telsim).
Well known online retailer in Turkey. They sell any kind of goods,
including books and electronics.
Some of the other lesser known retailers are:
Garanti Bank's online mall.
Retailer of general goods.
Mainly computer and electronics.
Retailer of technology products.
Novel idea that brings many conventional restaurants to the Internet.
They take your orders and fax (or email) it to the individual
Includes the online shop of a leading supermarket chain, Migros.
Online shop of a leading supermarket chain, Gima.
The mall contains some food shops.
Regarding your request on the data of the size of the online shopping
market... As the online population is still new to online shopping,
there aren't many researches and statistics on the subject. Still you
may find the following pages helpful for general Internet usage in
Turkey (note that many of the articles are in Turkey):
Published works, projects and master theses on e-Turkey.
Please feel free to ask for clarification on any part of the answer.
Hope this helps,
Google Answers Researcher