Scanning an object

I want to write a simple script that will check if a moveclip exists on the stage. If it exists, then some action should occur based on the objects position. If it doesn't exist, do nothing. I've run into issues with animate throwing errors for the object not existing, and also inconsistent results with the scanning. Here is some basic code:

if (athingtoscan)
{
trace("found");

// Some action
}
else
{
trace("not found");
// Do nothing
}

I've tried a number of different ways but can't seem to find one that works. What am i missing here?