I need to find a person's most recent email or phone number.
I have this person's full name, possible area of location. 
This is a urgent yet not hostile investigation, thus I would pay a
certain fee if needed but would not want to use method that would
seriously disturb that person.

Hello, there are a few ways to answer this. But since you asked for
the most-up-to-date way to find it I will say the internet is
definately a very easy way. This is assuming you know at least what
state they live in (and hopefully the city too, maybe the zip code?)
all of those will help narrow it down. Of course if the person has a
very odd name that it is not likely anyone else in the state has
(supercalaphragialisticexpialadocious) for example, than you probably
could just enter the state. Yes, I took that word from Mary Poppins
and it is probably spelled wrong.

Some webpages that offer phone number lookups are 

http://www.switchboard.com/

http://www.anywho.com/wp.html

http://www.lostpeople.com/

http://www.classmates.com

http://www.peopledata.com

http://locatersplus.net

If all of this fails, you can look up an old address of your friend
and talk to the neighbors or the family currently residing there, all
of whom may know something of their whereabouts. If you have an idea
your friend is living in a certain area you can check the city or
household directory. Most of these have been around for over 150 years
in most U.S. cities.  They are like telephone directories only much
more specific than a regular telephone director, as they offer names,
addresses, place of employment for all adults in the household, etc.
Most city directories are available in the libraries, but currently
more and more are making their way onto the internet. If you know
where the person went to high school or college than check with the
various groups there to see if they are still a member. Contact the
college directly if you must.