What's the difference?

What is the difference between "como estas" and "como estas tu" ?

No difference, but I think you need "a" before "tu." You usually don't add the "tu" though because it's obvious who you are referring to based on the "estar" conjugation. When using "usted/él/ella" forms, however, using "a usted" or one of the other phrases at the end is more common to clarify who you are referring to.

no need for the personal "a" before tú

Awesome, thank you for clarifying that!!!

Hola todos, ¿Como estás "tú" o como estás ? Ambos son igual. They are both the same.The "tú" is for for emphasis. Peter is right. No need for the personal "a" with "tú" Neither would you use the personal "a" when using the formal usage, it wouldn't be::¿Como está "a" usted? You would ask :¿ Como está usted? or "Como está? The "usted" implies more politeness and emphasis. Saludos, Rich

hola

Hola !!