For the items below, no in-depth discussion is required.  Just a
number, a short quote/excerpt and the reference itself would be great!
 Data must be recent, ie: 2004 or better.

1. Size of workforce in the US.  How many of these people are between
the age of 16 to 35?

2. How many people work in each of these industries: Retail, Food
Services (ie: Restaurants), Hospitality?  Also, how many of these
people are between 16 to 35?

3. How many people are using the Internet to search for jobs?  And how
many of these people are between 16 to 35.

I started on your question:

United States Bureau of Labor Statistics - THE EMPLOYMENT SITUATION:  MAY 2006
http://www.bls.gov/news.release/empsit.nr0.htm


1. Size of workforce in the US.  How many of these people are between
the age of 16 to 35?

ANSWER: 48,528,000 (approx)
NOTE: This number does not take into account age sector participation:
http://www.bls.gov/emp/emplab04.pdf

SOURCE:

US Workforce aged 16-34 - 33.7%  (2004)
http://www.bls.gov/emp/emplab09.htm

Total employment is at 144.0 million
http://www.bls.gov/news.release/empsit.nr0.htm


After that, your question gets very complex. 

Major industry sector
http://www.bls.gov/emp/empmajorindustry.htm

2004-14 National Employment Matrix, detailed occupation by industry
http://www.bls.gov/emp/empoils.htm


In any event, what I have done is free, perhaps another researcher
will take my links and extrapolate your figures for Q#2.

As far as Q#3, here's the BLS page with a mention
http://www.bls.gov/oco/oco20042.htm