You didn't even read your "web citations" which are actually someone found this Wikipedia page (http://en.wikipedia.org/wiki/List_of_United_States_extraditi...) and put some countries not on it in article form.

If you did, you would find the last one points to this PDF on the US Dept of State Website: http://www.state.gov/documents/organization/71600.pdf which is CHAPTER 209--EXTRADITION of CRIMES AND CRIMINAL PROCEDURE.

That lists Yugoslavia which isn't even a country anymore, but has a note

\1\ For the successor States of Yugoslavia, inquire of the Treaty Office of the United States Department of State.

Croatia is a successor States of Yugoslavia, however, I originally ignored that because I thought I'd have to contact the State Department. Then I decided to see if that info is published. Alright, Lets check out the Treaty Office of the United States Department of State.

Here's the Treaties in Force list.

http://www.state.gov/documents/organization/202293.pdf

Under Croatia it lists

JUDICIAL ASSISTANCE CROATIA — INVESTMENT Agreement on enhancing cooperation in preventing and combating serious crime. Signed at Washington February 16, 2011. Entered into force August 19, 2011. TIAS

That's pretty vague, but there is some agreement there.