Table Name As Function Parameter

I'm trying to write a function that I can run with passing the table name as a parameter. I want to return an integer. The tables wll be differnet types (different colums) but they all have a similar field that i want to get a count of. Someting alng the lines of this:

Create FUNCTION [dbo].[fn_GetItemsToPromote]
(
@TableName nvarchar(100)
)
RETURNS int
AS
BEGIN
Declare @SQL nvarchar(500)
return select count(*) from [@TableName]where promote = 1
END

It doesnt like the @TableName. Can anyone show me how to do this correctly?

Thanks!