Io completto mi arbore de Italiano!
You're right about "mio", but the article is not used in sentences like this one, so "grazie mio amico" or "grazie amico mio" are both correct :) The article is mandatory in sentences like "Sto ringraziando il mio amico", or "Sto dicendo grazie al mio amico", but not when talking directly to the person :)
I would add that "amico mio" (which sounds more natural to me) should be separated with a comma, because it's vocative and not the object of the phrase (reference: http://www.treccani.it/enciclopedia/complemento-di-vocazione_(La-grammatica-italiana)/)
Grazie, amico mio
Great job! I too have completed all of the Italian lessons. Now I review each day. I want new lessons. where do I go go from here? A while ago it told me with a certain number of additional poits I would reach the next level, but 13 days later and about an hour a day, I'm still not gettin to another level. How many levels are there?
Barbara - check out this link: https://support.duolingo.com/hc/en-us/articles/209669946-What-are-levels- . When this article was written, there were 25 levels. Each level is reached by completing lessons and/or by practicing. Hope this helps.