A locally populated forum such as this is indeed better than email or even a phone call.

If you phone the police you will have to go through a typically brief but time consuming process as you have to go through their call center computer. Your captors could hear you and then grab you while you are on the phone before you had a chance to explain your situation. A forum post is much more 'silent' and reaches a lot of people even when you are away and they can call the police for you.