Kahan kho gaye hain?
Not sure if it's right written, it means "where have you disappeared" but is it the formal/plural form? what would be the friendly form? Or the formal ? Or all of the possible forms? Here it doesn't say aap or tum... so I'm confused :(

Question

Kahan kho gaye hain? 
Not sure if it's right written, it means "where have you disappeared" but is it the formal/plural form? what would be the friendly form? Or the formal ? Or all of the possible forms? Here it doesn't say aap or tum...  so I'm confused :(

Answer

"aap" reflect mostly single person.
"tum" reflect bunch of person.

Kahan kho gaye hain?
Kahan means where.
kho means disappeared, lost

More phrase
1. Kahan chup gaya hai .
2. Koi dikhai nahi de raha hai.

check this link: http://www.linguanaut.com/english_hindi.htm
Good Luck :) :)

Answer

Namaste Leo ji,
Aap kaisi ho ? How are U ?

In this sentence ' AAP '  (you) is assumed (hidden)  since the use of GAYE (form of verb). If U R to make Past tense sentence :  TUM  KAHAAN  KHO GAYAA  or  THA.  However, invariably U use  AAP form to give respect.

By the way, Do U know the meaning of   KHONAA (root verb) ?
Pl get back to me.

For yr info  I am already registered as Hindi Teacher on this site.
Can't U see me ?
Would U like to have a Hindi session with me.
Pl cnfirm Whether U want to take it HERE or on Skype / ym / g-talk etc.
My id is ' mdchaskar '
Just add in yr contacts and inform accordingly.

dhanaywaad,
fir milenge,