Found Passport that was Reported Lost. Who Should I Notify?
Answer: If you report the passport lost, then it is deem invalid. When a passport is consider loss, the passport has no value. If you did not report it, the passport is still valid until the date it expires. The Department of State is the agency to report a loss or stolen passport.
Since you report to the State Department that the passport is missing, you will have to apply for a new passport using form DS-11. You must submit the form, as well as, all other necessary documentation at a passport acceptance facility. These documents include proof of identity, photocopy of the proof of identity, evidence of United States citizenship, and a recent passport photo.
Regular passport processing usually takes about 4-6 weeks to obtain a passport. You can use an expedite passport service which will process your passport within 2-3 weeks. To obtain a passport on the same day you apply, you will have to visit your closest regional passport agency, or employ a professional expediter to submit your application for you.
You can use the following link to further assist you on obtaining a new passport.
So, from the moment you report your passport was loss, it became invalid. Now you have two passports but can only use one for travel. Make sure you carry the right one when traveling. You can either safe keep the old one or discard it properly.