You can add a search page for custom content. Example lets talk about groups searching. We need a search page for type=groups.

This example is taken from /components/OssnGroups/ossn_com.php#L119-L133

<?php
function my_component_init(){
		ossn_add_hook('search', 'type:groups', 'my_component_hook');	
}
function my_component_hook($hook, $type, $return, $vars){
		//$params['q'] contain query string.
		
		$groups = new OssnGroup;
		$data   = $groups->searchGroups($params['q']);
		$count  = $groups->searchGroups($params['q'], array(
				'count' => true
		));
		
		$group['groups'] = $data;
		$search          = ossn_plugin_view('groups/search/view', $group);
		$search .= ossn_view_pagination($count);
		if(empty($data)) {
				return ossn_print('ossn:search:no:result');
		}
		return $search; 	
}
ossn_register_callback('ossn', 'init', 'my_component_init');

To add a menu item on search page see https://www.opensource-socialnetwork.org/documentation/view/5645/search-page-load