Internet Explorer Users
Take a look at this article that shows you how to setup Yammer as a search provider in IE for quick and easy Yammer searches.
http://www.erickraus.com/2014/03/yammer-search-in-ie/
Chrome Users
By the way, you can do this for Chrome if you just add the Yammer search URL to the list of Default search settings.
Just make sure your URL is in this format
https://www.yammer.com/[network]/#/Threads/Search?type=following&search=%s
where [network] is the domain of your network and the search parameter value is set to %s