To what extent were original papyri used as sources in the translation of the NIV New Testament? I am wondering to what extent original papyri were used in the translation of the NIV New Testament? I know there are some large papyrus fragments such as p45 and p66 and I am wondering how much the translators of the NIV referenced them directly.
The editors of the 2011 NIV write:


  The Greek text used in translating the New Testament is an eclectic
  one, based on the latest editions of the Nestle-Aland/United Bible
  Societies’ Greek New Testament. The committee has made its choices
  among the variant readings in accordance with widely accepted
  principles of New Testament textual criticism. Footnotes call
  attention to places where uncertainty remains.


I believe that at this time the 27th edition of the Nestle-Aland Greek New Testament would have been the latest.  Metzger's Textual Commentary on the Greek New Testament lists the following papyri as the most important witness texts for this edition:


P20 - 3rd c.
P23 - 3rd c.
P29 - 3rd c.
P38 - c. 220
P45 - c. 250
P46 - c. 175-225
P48 - 3rd c.
P50 - c. 163-172
P66 - c. 200
P69 - 3rd c.
P75 - c. 175-225


Since the editors state that they based their translation on the Nestle-Aland text, they would have at least considered the above in their translation.  A full list of the available papyri can be found here.

You specifically asked about papyri, so I took your question literally.  All of the above texts are fragmentary and sometimes don't even include complete chapters.  The only complete Greek New Testament texts from antiquity (as far as I know) are the codices, listed here, the earliest of which date from the 4th century.

(There is, of course, no guarantee that the age of a text is any measure of its "authenticity" in the sense that it is faithful to some "autograph".  There is no way to know whether there are some still earlier texts that are lost.  The Nestle-Aland text makes educated guesses about what might be in the supposed "autographs" by considering all of the available manuscripts.  The actual text used by the Greek Orthodox Church today follows fairly closely what is found in the majority of the available manuscripts, which varies widely in places from the Nestle-Aland "Critical Text".  Some of the Orthodox readings are quite different from what is found in the NIV).