They have the proper access and resources to change the status of your home on Trulia.
Trulia prefers "Homes for Sale" to be represented by real estate brokers to assure the quality and integrity of the information.
Trulia is a "syndicated" service. Which means it pulls it's information from the MLS IDX feeds.
So, when a Realtor places a listing in the MLS for their area, a few days later Trulia will syndicate or "sync" with that information. It is then your home will show as "For Sale" on Trulia.
If you are not listed in your local MLS with a Realtor in your area then you will not see your home as "For Sale" on Trulia.
If you are listed with a Realtor and your home is not showing "For Sale" on Trulia then you need to contact your agent and let them know. The agent can simply create and/or sign in under his/her account and add or update that listing information for you.
Sorry, but you are not able to do this as a "shopper" or "viewer" on your own on Trulia, that option is only available to Realtors.
Hope this helps to clarify what the other agents below were speaking of.
Good Luck with your sale!