The pin marked
Vin on the TeensyLC board is equivalent to the
Vin pin on the Arduino. The pin is designed to be used to supply power to the Teensy board. However based on the description page to which you have linked, it appears that the
Vin pin can also be used to supply 5V to an external circuit when the USB port is connected. As far as I can tell (and you could check with a DMM in continuity mode), the
Vin pin is tied directly to the USB 5V pin.
It is important to note that the TeensyLC runs at 3.3V. None if its I/O pins are not 5V tolerant - in other words hooking up a 5V output directly will damage it. There is one output-only digital pin on the board (D17) which has a level shifter on-board so that it can provide a 5V level logic output signal (not power).
You will need to ensure that the output of your sensor is correctly limited to 3.3V to avoid damage. This can be very easily be done with the sensor you have. Your sensor does not require 5V, in fact one side is an LED which has a forward voltage of 1.5V at 20mA, and the second side is a photo transistor with a pull up resistor. You can simply hook sensor circuit you show to the 3.3V supply instead of to 5V and it should function correctly. You may need to reduce the 200R resistor down to something closer to 100R to account for the lower supply voltage.