If you uploaded your searchresults.php file to your forum root, such as
www.mysite.com/searchresults.php and your error message is this:
Warning: chdir() [function.chdir]: No such file or directory (errno 2) in /home/m****/public_html/searchresults.php on line 8
then the data you enter in the chdir('/path/to/your/forums/'); would be
chdir('/home/m****/public_html/');
(of course you would want all the information there)
and not
chdir('/var/www/vhosts/mysite.com/');
The second one - /var/www/vhosts/mysite.com/ was an example.
Hope that helps