Use IN sql query Stored Procedure & retrieve data

ALTER PROCEDURE dbo.StoredProcedure2

@userid varchar(500)

AS
BEGIN
SET NOCOUNT ON

DECLARE @SQL varchar(600)

SET @SQL =
'SELECT  USER_NAME, FIRST_NAME, PASSWORD, LAST_NAME, MIDDLE_NAME, SRNO FROM  USER_MAS
WHERE SRNO IN (' + @userid + ')'

EXEC(@SQL)
END

 protected void BtnSpIn_Click(object sender, EventArgs e)

    {

        SqlDB objDB = new SqlDB();

        objDB.Prepare("StoredProcedure2", CType.StoredProcedure);

        objDB.AddCmdParameter("@userid", DType.Varchar,"1,2", ParaDirection.In, false);

        DataTable objDT = new DataTable();

        objDT = objDB.ExecuteCommandDataReturn(); 

    }