Okay, all kidding aside I can see this as a problem that needs solved. Being social is really the same behind a keyboard as it is in front of a person. That being said there is the level of comfort of being able to "get away" without feeling awkward if the person is a creep.
The best way to keep a conversation going is to end what ever you say with a question. Not always just a closed ended question but a simple open ended question will do.
Thoughts, Opinions, Input, Emotions, Decisions, are you starting to understand? (Closed Ended)
Really it is harder to keep a conversation going online then offline (fine tuning your social skills) because there is the missing very important element of body-language. Keep on topics that you are both interested in.
Keep online conversation short 10-15 minutes, end in questions, say off the wall stuff, not offensive just crazy things to keep the mind going.
I take it this is for online dating conversations.