code: public function lookupUser($user_id)
  	{
  		$request = new UserRequest($user_id);
  		$this->emit('request.user', array($user_id));
  		$response = $this->post($request);
  		return new UserResponse($response);
  	}
docs: Lookup user information from user id
  
  @param  string  $user_id
  @return UserResponse