If you decide to use a logo design with the Facebook logo included, you'll need to receive permission from Facebook first:
https://www.facebook.com/brandpermissions/logos.phpNumber six in the guidelines suggests that using the Facebook brand will not be approved:
"6. You may not combine our Brand Assets, or elements of our Brand Assets, with your own name or mark or generic terms."
Sorry to put a damper on the contest, but I thought I'd pass this information on before anyone else includes the Facebook brand in their entries.
While there are distinct similarities, Facebook does not own the letter "f", and my submissions utilized a sans-serif typeface that is free/public domain as well as hues that are similar to, but not identical to, the Facebook colors. There are arguments to be made that these marks follow the Fair Use laws of the United States, as well as arguments supporting trademark infringement according to Nominative Use laws of the United States.
If this is a concern for Trudi, one of my submissions does not utilize the "f" that is similar to Facebook's, so no worries there.