Click on the top most site or folder in the Site Manager.
On the menu bar, click Tools > Site Manager > Find Text in Site Manager.
Type in some letters from the site name.
Click OK.
If the site you wanted wasn't highlighted, click Tools > Site Manager > Find Next, until the desired site is highlighted.
The Find Text in Site Manager tool is not case sensitive, will only search from the top to the bottom of your site listings, and does not recognize wildcards.