Ok - when I look at the Newsfeed main page, my Outlook Find is greyed out.

Any idea as to how I can make it active again?

What I want to be able to do is search within my posts without having to do an Advanced Find.

Any ideas?

That's an Outlook-ism, unfortunately.

When you're viewing a HTML page in Outlook (like the NewsPage), the find button is grayed out.  Workarounds would be either turn off the NewsPage, or click on a different folder.  Not great solutions, I know...