Facebook no longer supports custom parameters in sharer.php
The sharer will no longer accept custom parameters and facebook will
pull the information that is being displayed in the preview the same
way that it would appear on facebook as a post from the url OG meta
tags.
Use dialog/feeds instead of sharer.php
https://www.facebook.com/dialog/feed?
app_id=145634995501895
&display=popup&caption=An%20example%20caption
&link=https%3A%2F%2Fdevelopers.facebook.com%2Fdocs%2Fdialogs%2F
&redirect_uri=https://developers.facebook.com/tools/explorer