Talk to your attorney. In some jurisdictions, you only need to notify the creditors and keep proof of the notice. This is only true if no creditor received money. In other jurisdictions, you need to add the creditors to a closed case. In still others, you have to pay $260 to reopen the case and add the creditors. There is no time frame to do this, but you should act quickly before the creditors without knowledge try to collect from you.
[This communication is intended as general information and not specific legal advice, and this communication does not create an attorney-client relationship.]
In Connecticut jurisdiction (where I practice) you only need to amend to add them if the case is an asset case. If there are no assets to distribute, it is not necessarily a fatal flaw. You need to talk to your attorney who helped you file. But more than likely he may tell you that you can send them the 341 notice to let them know that you have filed and are discharged.
This is a common question. In Conn. the bankruptcy court has decided that in no-asset cases, the discharge is effective against any creditor (even one that was inadvertently omitted from the schedules) upon notice. So, first contact your bankruptcy attorney, and second mail each creditor or collector a copy of your bankruptcy discharge. That should do the trick, unless your case was an asset case.