How To Continue A Conversation?

Yesterday I met one of my old friends on line. He was a special person to me. We had been classmates for five years. There were a lot of things happened during our high school time. I was glad that we could chat lightly together, but the only thing that I didn't know how to improve is: I couldn't continue a conversation. It's one big problem that I've troubled with. Whenever people try to make a conversation with me, my answers will end it. Because of my easy, short, and brief answers, people wouldn't know how to keep it. I understand this situation, but I just don't know what else I can say. Maybe I should practice it frequently.