...is most appreciated in the shape of a handwritten letter, of course.
But I am realistic and looking forward to an email or a friendly 'hello' instant message as well. If I cannot identify an instant messenger request in any way, I might not react though - I love to chat, but I also like to know who's knocking at the door. So if you stroll around as "sugardaddy69" and want to chat with me, you better reveal your identity to me in an appropriate way (e.g. email) beforehand - so I know who it is.
And yes, I am in social networks, but to be honest: I will always prefer to get in touch through instant messaging. Facebook and the like are becoming more and more like graveyards of friendships – once I've accepted a friend request, I never hear (directly) from him or her anymore. Bottom line: I prefer one to one communication.