Load one of your sites. You can use the developer console in any modern web browser (Chrome or Firefox are best) to check the following (hit F12, and use the magnifying glass or investigate tool to look at a part of the DOM that should have that font, like a
<p> This should be in that font </p>
Is the CSS rule showing up on the Elements tabs style sub-tab??
If so, is there another CSS rule over riding it?
If the rule is definitely loaded, with the developer console open, go to the Network tab and reload your site. In this tab, you should look for your file 'customfont.ttf' and see what the Status code is. You're looking for 200 or 304 to verify the font was loaded.