Just a knife?
Guns I don't play with, but if you try and rob me with a knife I'm going to take it from you and use it on you. (then again I do have 10 yrs of martial arts training)
You can't outrun a bullet, but if someone pulls a knife on you scream your head off and run like heck. He's not going to throw it at you, this isn't the circus and you aren't strapped to a spinning wheel. Once you draw enough attention the guy will bolt like a scared kitten.
Thieves are bottom feeders. They don't like attention. Once you make a scene they take off like someone lit a fire under them. Even if they don't, YOU CAN. It's just a knife...... take a sprint. You have enough adrenaline to achieve speeds you never knew possible if you are truly scared.
Sorry to hear about it though........GL on recovering it.