I have thin hair as well and wear all sorts of fake hair.
Snap in extensions are easy to get hold of (ebay!) also clip on ponytail extensions are fairly cheap on there and look decent. Full on wigs are also good sometimes (see avatar) - I cut the fringes off mine and wear them half way back on the head (seam covered with a ribbon headband) and people seem to be fooled...or pretending, and calling me wiggy behind my back
xx