Towamencin police have arrested a township resident and are searching for another in an insurance fraud scheme.   Investigators say 30-year-old Ian Crotzer of Monroe Drive reported his car stolen last month when in fact it was in a Morgandale Condominium garage owned by alleged accomplice Sterling Hall.   Police say the idea was for Hall to get rid of the car so Crotzer would no longer be responsible for the monthly payments or insurance.   Crotzer is free on bail.   Hall remains on the loose.