First you should search for a buy and sell on your area or country. You can try posting your products on ebay. ALso, I would likely suggest to start on social networking sites since many internet users really spend lot of time scrolling their newsfeed on facebook, twitter, instagram and other sites. Among them, I think the most site that had the largest number of users is on facebook, and personally, I have purchase many products on facebook, some of them are just random, it just happens when a post pops up and being influenced by the comments and me ending finding myself buying the product. Also you can try on instagram because it becomes a popular site to advertise and sell your products by taking great pictures of them.
But of course it depends on the kind of product you are selling and what kind of your target customer.