Rails form_tag to show action

I have a Rails app where I have a partial that I want a dropdown in so when a user is selected it will do a get method to the urls /timecards/:user_id which will be the controller's show method passing in the User's id field. I'm having a hard time with my paths in the form_tag and could use some help.

Here is my partial in the view:

<%= form_tag timecard_path, :method => :get do %>
  <%= select_tag options_from_collection_for_select(User.employee.order("username ASC"), :id, :username) %>
  <%= submit_tag "View Employee", class: "btn btn-primary" %>
<% end %>

From rake routes I get the following output:

timecards GET    /timecards(.:format)                 timecards#index
                           POST   /timecards(.:format)                 timecards#create
              new_timecard GET    /timecards/new(.:format)             timecards#new
             edit_timecard GET    /timecards/:id/edit(.:format)        timecards#edit
                  timecard GET    /timecards/:id(.:format)             timecards#show
                           PUT    /timecards/:id(.:format)             timecards#update
                           DELETE /timecards/:id(.:format)             timecards#destroy

Here is my controller: timecards_controller.rb

class TimecardsController < ApplicationController
before_filter :disallow_clients, :disallow_medics, :disallow_employee, :disallow_supervisor

  def index
    @clock_events = ClockEvent.includes(:user).search(params[:search])
    respond_to do |format|
        format.html do
          @clock_events = @clock_events.paginate(:per_page => params[:per_page] || 20, :page => params[:page]).order('users.username asc').order('clock_in desc')
        end
        format.csv { send_data ClockEvent.to_csv(@clock_events.order('users.username asc').order('clock_in desc')) }
      end
  end

  def new
    @clock_event = ClockEvent.new
  end

  def create
    parse_times!
    @clock_event = ClockEvent.new(params[:clock_event])

     if @clock_event.save
       redirect_to timecard_path(@clock_event.user.id), notice: "Entry added for #{@clock_event.user.username}".html_safe
      else
       render :new, notice: "Time Card Entry failed to Save".html_safe
      end
  end

  def show
    @user = User.find(params[:id])
    @clock_events = @user.clock_events.search(params[:search])
      respond_to do |format|
        format.html do
          @clock_events = @clock_events.paginate(:per_page => params[:per_page] || 5, :page => params[:page]).order('clock_in DESC')
        end
        format.csv { send_data ClockEvent.to_csv(@clock_events.order('clock_in desc')) }
        format.pdf do
          pdf = TimeCardPdf.new(@clock_events, @user)
          send_data pdf.render, filename: "timecard-#{@user.username}",
                                type: "application/pdf",
                                disposition: "inline"
         end
      end
  end

  def edit
    @user = User.find(params[:id])
    @clock_events = @user.clock_events.search(params[:search]).order("clock_in ASC").paginate(:per_page => 10, :page => params[:page])
  end

  def update
    parse_times!
    @clock_event = ClockEvent.find(params[:clock_event][:id])
    if @clock_event.update_attributes(params[:clock_event])
        redirect_to edit_timecard_path(@clock_event.user.id), notice: "Updated Successfully".html_safe
    else
        redirect_to :back, notice: "Woops.".html_safe
    end
  end

  private

  def parse_times!
    params[:clock_event].parse_time_select! :clock_in if params[:clock_event].has_key? 'clock_in(5i)'
    params[:clock_event].parse_time_select! :clock_out if params[:clock_event].has_key? 'clock_out(5i)'
  end

end

So I believe I'm calling the path properly in the form_tag but when I load the page I get the error: No route matches {:action=>"show", :controller=>"timecards"} Even though there is a show action in the timecards_controller.

I think something I have to set the form_tag for an explicit url and somehow pass in the :id of the user in the params. But I'm a bit stuck on how to do this.

So to summarize. When I have the dropdown, I select a user, click "View Employee", and that should go to the show action in timecards_controller.rb with the url of /timecards/3 (as an example). I've never used form_tag in this way before so passing a path or explicit url is a bit foreign to me.

Any help you can provide would be greatly appreciated. If you need further clarification or have questions, please ask.