Google-drive – Is it possible to automatically re-share files shared to a Google account

The information that you are giving us is the link to the folder - not the link to the individual files within that folder.

That is why "anyone with the link" can get to the folder, but cannot get to items witin it, ie because they do not have the links to the items in the folder.

Arguably this is a silly distinction: if you want "anyone with the link" to see the folder, then surely you're implying that you've given them the file links, too. But this isn't how Drive is working at the moment, according to testing I just did in Chrome.

Right now, if you want me to see the contents of files in your Google Drive folders, then you have to give me the link to theose files, not just to the folders.

(This may be different if you set permissions to Public on the Web - if you want to test this, set up a folder and I'll take a look.)

Update
I guess Facebook heard you because just 1 month after you posted it, it now happens by itself when you click "share" (unless you uncheck the option). Well, as long as you abide by the following rules:

1. The secondary post must be completely public.
2. The original item must be an external link and not a Facebook post.
3. You share the secondary post on a wall (yours or anyone else's) and not in a private message.

If you stray away from any of these rules, the original answer still applies.

Original answer
Officially you can't. Facebook treats it like a comment of sorts, so it's just like you can't officially share comments.

However, you can "cheat" Facebook by sharing the literal link i.e. instead of the share button, get the URL from the post's timestamp:

For example:

Hey everyone, see what my friend wrote:
http://www.facebook.com/ID_of_the_friend/posts/post_ID

It doesn't offer a preview, but it works...