12 days late. My cycle is normally every 24 days, I was supposed to get my af on 12/17/2011 but there has not been any sign of af coming on. I took 5 hpt and they are all negative... I'm still waiting on my bfp

Some women's cycle can be thrown off by sickness etc. Or just tour body. Wait a bit your peroid might come. Or go see a dr.
Also home tests don't always work. It depends on the amount of hormons you are giving off.

It really may be just one of those things; I once missed 3 in a row and no reason was ever found. Stressing can affect it too; the more you worry the more your mood will affect your hormones. Have you had any emotional upset lately ? Or been ill ? If you are continuing with pregnancy tests, try different ones from different stores, or have the doctor's surgery do one for you. Pregnancy is often accompanied by signs such as nausea, breast tenderness etc, even in the very early stages. Have a good look at, and listen to, your body. Also, are you middle-aged, or very young ? Periods can go suddenly haywire in both age groups

Its still possible. Some people can be pregnant for weeks and still have to wait longer to get a BFP because their hcg levels. You could have just tested to early anyway, which that could very well be the case. My first pregnancy I didn't get a BFP until I was 18 weeks along with just a home urine test and than with my daughter I was only 5 weeks. Most peope find out any where from 5-8 or 9 weeks. Some even have to wait a couple more weeks. And than you have the select view that can find out around 2-3 weeks but you can't count on it. Try another test in about another 1-2 weeks and if you still get a BFN than call the doctor and have a blood test done if you still expect pregnancy or don't have a period still. Good Luck!