If you want to use trim paths you need to make sure that the lines you imported from illustrator have no effects or brushes applied. Simple stroked paths will convert to a stroked path. If there is a brush applied or any other funky stuff going on with a stroke it imports as a closed path with no stroke.
Sometimes the easiest thing to do is to go to the Illustrator file, duplicate the layers that you have that you want to reveal with trim paths, remove all fills and brushes from those paths, convert them all to 1 point stroke, then import into AE as a comp, convert the converted paths to shape layers, edit the width for each of the strokes until they cover the original artwork, then apply trim paths and use the converted vector layers as track mattes.
There are no plug-ins that I know of that will do the same thing. You're just going to have to rework the files a bit or do a bunch of tracing.