The actors who play Draco Malfoy and Neville Longbottom are on Twitter (Tom Felton and Matt Lewis) but as far as Facebook goes, I'm not sure. Try searching it.
yes
Because Harry Potter Is a Wizard And Wizards Don't Use Computers. There Are Fake Harry Potters On Facebook Though. :)
Some of the cast will be there, but ONLY for the Grand Opening.
Yes they do have facebooks.
no
If you mean Selena Gomez, then no she has never been in the Harry Potter cast.
Yes it's new this year "A Celebration of Harry Potter" where some of the cast go to the park for about three days at the most and do interviews and autographs.
Nobody from the Harry Potter cast died in a car crash.
Harry Potter spells are fictitious, they do not work in real life.
All of the parts for the 7th Harry Potter film have already been cast.
Fiona Weir.
If you have the right connections!