Hi,
For the past month and a half or so, I have been running at least 40 minutes everyday. For me, this means I can run anywhere from 3.5 to 6 miles. Afterwards I always do some light ab work. However my results are less than satisfactory, and I have not lost any weight. I read somewhere that I should begin weight lifting to see any results is this true?

Thanks, any advice is welcomed

Even if it werent true (which it is because weight lifting improves metabolism), EVERYONE should be lifting some weight. Strength training is invaluable. Helps in every way. If you have lost weight and youre running a lot, perhaps youre eating too many carbs or too many calories altogether.
Also, long distance running is known to be catabolic (i.e. it burns muscle as well as fat). If your main goal is fat loss, look into a form of cardio called HIIT. Means you only have to run for 5-10 minutes depending on your level of fitness and you'll burn fat (and keep muscle) better than you would with long-distance.

Most importantly, how does your diet look? Are you eating 6 small meals instead of the traditional 3 square meals?