You must pray, addressing God with 'Thee' or 'Thou'.
Seriously - i've heard people claim God doesn't listen you unless you pray this way, and know a few speakers who've been 'spoken' to at the door because they haven't addressed God in this way.
We boldy approach the throne of grace through Christ!
It is because of Him alone that the Father hears our prayers. While certain things may hinder our prayers (1Peter3:7) there is no mantra or magical formula to praying. We simply cry unto our Father in the name of Christ, because of Christ.
It's A Non-Issue
Let me just add that there is no reason why a person shouldn't address God with thee or thou (though in our culture it maybe sounds like you are speaking in tongues). Our wording is just a non-issue. Of more importance than the words we say are the work of Christ upon us and the cry of our heart behind the words. We can mumble an incoherent prayer from a heart that loves and yearns for God, or we can speak eloquent prayers from a cold, hard heart that has lost its 1st love in favour of tradition & legalism.
[Additional Note: That we actually pray is perhaps a bigger issue]
More Important Battles
There's more important things to squabble over - like what we wear or the Bible version we read; Hymn books or powerpoint, organs or guitars . . . . . . But we rarely, if ever get into long and deep discussions about the person and work of Christ.