Cat lost in wall cavity in house?

i have had a 5 month old female cat , Tiffany , for 4 days. it spent the first 2 nights behind washing machine. on the 3rd day , we seemed to bond,& she finally ate , & accepted lots of stroking etc. i blocked all access to behind washer , but this morning i noticed the board under the bathroom sink was moved. there is a n entrance that she probably squeezed in,that leads to boxed in pipes & then behind toilet & then a full ceiling space above the kitchen. there will be 2 sets of light fittings in there. i have not heard a sound , after lots of enticing & putting a bit of tuna at the entrance,there has been nothing. to get at the area would mean taking a ceiling down ( no way ),i fear the worst. anyone got any ideas ??