Well there are several circumstances....
ie a guy most times are attracted by looks first, he might be very
interested in knowing her and if he knows who she is, he will ask
his friends for her numbers or setup a meeting.
If the guy is very interested and does'nt know the gal at all, then
he would naturally go up to the girl and ask her for number if he
has the courage to.
There are some guys who like to take it slow, although they might
be interested in a girl, they will first be friends for a while
then start dating....
Whereas others, just want to start dating the girl asap by asking
her out for a date the next day.
And then there's the good friends for a long time, then the guy
realizes he likes his good friend.... that one depends...
If you really want to find out whether the guy likes you, then go
ask your friends to ask his friends thingy... or just be brave and
ask him... or if you like to be childish, then do the secret
admirer thing, email or write him letters...