You can post them on any site, although expect some sites to ghost your comment (YouTube) or report your posts as spam (Facebook).
In the case of Facebook, if you were to post your affiliate links on your own fan page, people would be less likely to report your post as spam as long as the product is relevant to the page.
On the other hand, creating YouTube videos and posting your affiliate link in the description is another method you could use, but posting them in the comments section is not a good idea for the reason I mentioned above.
Of course, whether or not direct linking without shortening the URL or directing the traffic to a squeeze page first would result in higher conversion rates is something that you'll have to find out for yourself.