Changing a page's URL
1.Navigate to the page whose URL you want to change.
2.From the More drop-down menu, select Page settings.
3.In the box below Page URL, type in what you want the last part of the page's URL to be. (Note, the beginning part of the URL is dictated by the structure of your website. For example, if you want to add a page URL of "World" to your site, which you called "Hello," the page's full URL would be //sites.google.com/site/Hello/World.).
Or try service called GPlus.to which allows you create a short URL which redirects to your Google Plus page