ask him out via facebook or face to face?

[Liana]

theres a guy im mad about - it's official. he comes into my work for lunch as he works up the street and when he does i can barely stand - he actually makes me weak in knees.

it's now been 5 months of flirtation and i cant handle it anymore - i wanna ask him out but my friend said not to do it in person cos it would be putting him on the spot! he said to do it via fbook but there are two issues

a) i know his last name but he doesnt know that...
b) he's not even on my friends list and i think it's extra stalkery!

help! wahhh
my friend who gave me advice is a man - a gay one lol.
we're never really alone cos he only comes into my restaurant to eat, usually with co-workers. maybe once i can catch him while he's paying for his food at the counter alone etc but i cant get more private than that unless i follow him to the loo lol