Never convert the date formats to string whenever you are comparing. When you do this the date behaves as a varchar value rather than the date, hence the comparison works on varchar.
Use the following query.
declare @date nvarchar(10);
set @date='01/12/2014'
select convert(varchar(10),datevalue,103) from Table_1
where convert(datetime,datevalue,103)>convert(datetime,@date,103)
Hope it solves your problem.