try this one
<div class="pinit" onclick='window.open("http://www.pinterest.com/pin/create/button/?url=http%3A%2F%2Flocalhost%3A8080%2FHowl%2FHome.html&media=http%3A%2F%2Fi.imgur.com%2FToZz7PB.png&description=Howl%3A%20Share%20Your%20Life","Pin It","width=300,height=300,top=0,left100")'>
provide name and properties to your new window.
,"Pin It","width=300,height=300,top=0,left100"