There is a very subtle difference, for example: I'm thinking of you would normally be used in a situation where that person is having a hard time, maybe they are ill, or a family member died. (there is no specific thought) I'm thinking about you would normally be used if you like someone and you tell them you are thinking about them in a nice way, (there is a specific thought - like going on holiday together). Here's another example: Your friend wants to do something tonight and says; "What should we do tonight" and you say "I'm trying to think of something" I'm trying to think OF something means there's nothing specific you are thinking about because you are trying to find an idea (non specific thought). Thinking ABOUT something means you already know what you are thinking about. (specific thought) I'm trying to think OF something = you are trying to think of an idea. I'm thinking ABOUT something = you are thinking about that specific idea. hope that helps! Rebecca

In the example you gave, the meaning is almost exactly the same. Usually if you think of something, it's an idea just came to your mind. If you're thinking about something it's probably been in your mind for some time. "Can you think of anything?" is asking for an idea, or a solution to a problem. "Can you think about it?" is asking someone to consider an idea that already exists. Thinking "about" something is a longer, more continuous action. However, when talking about people we often use "thinking of you" to mean "thinking about you" It's easy to see why this would be confusing to people trying to learn English. I hope this answer helps you a little.