I am interested in reaching (email or snail mail) the owner of the
abandoned building at 2123 F St, NW Washington DC 20037.  Also, I
would love to know if it is for sale and if so, how much.

Dear johnbentley,

I successfully found the name and the mailing address of the the owner
of the said property. Since it is a private individual, I am not
allowed to provide that information direct in this answer due to the
strict Google Answers privacy regulations.

However, I can provide you detailed instructions on how to get the
contact information. Please follow this link; it will take you to the
Real Property Assessment Database of the Washington D.C. Office of Tax
and Revenue:
https://www.taxpayerservicecenter.com/RP_Search.jsp?search_type=Assessment

Only fill the "Premise Address" fields of the search form:
"Street #" (2123)
"Street Name" (F)
"Thoroughfare" (choose ST from the list)
"Quadrant" (choose NW from the list)

Then, click the "Search Now" button. You will get the search result.
Click the underlined lot number "0080 0802", and you will be taken to
the detailed property data set, including the name and the mailing
address of the current owner.

As for whether that particular property is for sale: Unfortunately, it
is not possible to answer that question since there is no centralized
and/or authoritative source listing such information. But I am certain
that the current owner, should she be interested in selling the
property, will gladly let you know upon request.

I hope that this will be helpful!
Regards,
Scriptor