I lost my iPhone

You can't find the phone using the serial number. You need to recover your Apple ID and password.

See if you can recover the ID/password. Use every email address you can think of.

Apple ID - How to find your Apple    An iCloud e-mail address is an Apple ID.

Apple ID - Find              

If you forgot the Apple ID password, enter the Apple (iCloud) ID, and click Forgot Password. See if you can get an email option if necessary.

Apple ID - Manage            

Apple ID – Forgot Password            

Then you can use Find My Phone.

Find My Phone - Lock and track your device using Lost Mode.       

Find My Phone - If your device is lost or stolen.