"You are my pretty young girl"
Tu es une belle fille.
Tu connais...? is french for do you know....? It refers to a person.EX: Tu connais la jeune fille?Do you know the young girl?Hope this helps!
Tu est tres belle
Tu es / vous êtes une belle fille. "vous êtes une jolie fille" or "vous êtes très belle / très jolie"
Tu es tres belle, ma valentine.
vous êtes très belle - or- tu es très belle = you are very beautiful - bisous are 'kisses'
Tu es la plus belle fille du monde
for a girl, "tu es belle" or "vous êtes belle" for a boy, "tu es beau" or "vous êtes beau"
(vous ette tres belle) or if you are very close to or more personally involved you would use tu instead of vous. They both mean you but tu is much more personal ( tu et tres belle) for example a close friend or family as opposed to a business associate or an aquaintance or some one youd meet on the street
You are very beautiful and I want to be your friend.
Very beautiful, Darling. You are adorable, what a beauty!
Assuming you are speaking to a girl... Familiar: Tu es tres jolie... Formal: Vous etes tres jolie... Also, Jolie can be replaced by "belle" (beautiful)