Trulia does not allow FSBO postings. This is a help forum on the subject:
My home is for sale or rent. How can I submit it to Trulia?
If you are a home owner and wish to submit your listing to Trulia for sale, please note that we don't accept FSBO listing submissions at this time. However if you are working with a full-service or flat-fee listing agent or broker, he or she can submit your listing to us.
If you are a home owner and wish to submit your listing to Trulia for rent, you will need to indicate that you are a landlord in your Trulia profile in order to submit your listing to us.
Both submission options can be found at http://www.trulia.com/submit_listings/.