Hi,
The voltage follower (common collector) is known for it's large voltage drop. The problem stems from the drive voltage however, not the transistor itself. With a DC supply voltage of 12 volts and a drive voltage of 12 volts (directly on the base) the emitter must be around 0.7v down from 12 volts. That's because the base emitter drop is around 0.7 volts. So the best you can do is around 0.7 volts that way. Since yours is 1.34 volts, you should be able to do better than that.
However, with a common emitter topology (PNP emitter goes to 12 volts or NPN emitter goes to ground and collector is output) you can get as low as 0.2 volts or even better with some modern transistors made for low Vce. Check out that configuration and see if it works better for you.
If you connect the NPN emitter to ground and drive the base with say 1k, the collector voltage will drop as low as 0.2 volts or so, so connecting the fan to the collector and to the positive supply rail (12 volts) you'll get a much larger voltage output.
The advantage of the voltage follower is you can get nice control over the output voltage at the emitter. If you dont need that however, then a common emitter configuration is better.
If you need to control the voltage output then a slightly better circuit would be in order...possibly by using two transistors instead of just one.