I'm an only child, too, and used to spend a lot of time as a child at my neighbour's house where there were four offspring. Their house always seemed so lively and 'informal' compared with my silent house (apart from the clock ticking!).
I don't think I felt particularly lonely, I could always amuse myself by reading, but like Lona I've always been shy - excuricatingly so, in fact! My 'little school' was predominantly Catholic, so to be an only child in amongst families of 6-14 children did feel a little odd!
As an adult, the only time that it's cropped up was when my father was nearing the end of his life and a friend, who was wonderfully supportive, commented that this was one time when having siblings for support would have been good. It had never occurred to me to ask anyone for support! Of course, it wouldn't necessarily follow that one would get support from family anyway . . .
I wonder if being independent is a trait that is more likely to develop if one's an only child? No-one to fight your corner?
Back to the OP, 'virtual' friends are no substitute for real friends, you need physical social interaction. How else do you learn to cope with other people and their actions?