According the Pons dictionary, dank as preposition takes only the dative case but the free dictionary says it takes either the dative or the genitive.
In order to understand this confusion, you can first read this question about the condition of the Genitive case in the German language.
Briefly, I can say that the genitive is not as popular as it used to be. Because of this reason, you can hear / read dank with the dative case almost everywhere in contemporary texts and speeches.
I have always used dank with the dative case. I would also say dank dir.
Some examples of dank with the dative case:
Dank seinem Fleiß hat er die Prüfung bestanden
Das Kind erreichte das Ziel dank seinem Vater
dank deinerhas to be followed by an object to make sense. It's equal toThanks to your.... ExampleDank deinerschnellen Hilfebin ich jetzt viel früher fertig. You could also sayDank dir bin ich jetzt viel schneller fertigwhich puts the focus more on the person responsible than on the action. – trixn Jun 29 '17 at 13:14Danke deinerdoes not need an object ifdeineris not a possessive pronoun but the genitive of the personal pronoundu. This usage is very rare, but grammatically orthodox. – Toscho Sep 20 '17 at 20:46