The reason for this Placeholder not being found is because of this line
`Visible="false"`
while defining the ASP.NET control
Visible="false"
does not render the element in the First place.
So you have no way of selecting it. Instead remove that line and add a Class to it which has the display property set.
So by doing this the element will be available on the DOM
and your selector should work fine.
<asp:Placeholder runat="server" ClassName="hide"
CSS
.hide{
display: none;
}