i don't know if such a plugin exsists, but you need to call only one function to do that!

$options = array('owner_id'=>integer, 'type'=>'object', 'subtype'=>'blog', 'count'=>false, 'limit'=>integer, 'offset'=>integer);

elgg_get_entities($options);

Now you need to figure out a way to obtain the owner_id, that can be made by a search or a user picker

you can include the code in the blog plugin, or better create another plugin with that code, you can for example add a menu button in the blog plugin that redirect to a page that shows the blog entries obtained by the search