The definition of flirting is to behave as though you are sexually attracted to someone, but in a playful way rather than with serious intentions. If you are chatting online, you would obviously not be in the presence of the person you are speaking to, so you would not be able to see their body language or make eye contact. The question is why would you want to flirt at all? Just for your own amusement and entertainment? If the person takes you seriously you may end up with an uncomfortable and awkward situation which you had not intended to arouse. It is better to be truthful and speak sincerely, rather than playing with the emotions of another person.
Flirting is fun, and can lead to healthy dating and relationships, but different people perceive flirtatious messages in different ways. Online flirting is made more difficult because of its almost exclusive focus on words, when more than half of communication in real life is nonverbal and usually perceived only semi-consciously. Flirting through a chat program usually means giving personal compliments and using a lot of emoticons, but can also be achieved through well-constructed sexy jokes. Humor that employs the use of the double-entendre is risky and should be used sparingly. Instead, try self-deprecating humor or jokes that flatter the person you hope to impress.
Flirting online is so much easier than in person. You avoid the self-consciousness of having to look the person in the face and you time to think before you type. Online flirting is just showing an interest in someone, joking and being really friendly. It’s teasing them a little as well. I would be careful though as you don’t really know much about the other person and they make take it more seriously than you intend it to be.