I recently purchased a 20 year old townhouse with a single unit heat pump. Now that the weather is changing, the unit is not heating the home. The blower is on but the air remains cold. Is there a pilot light that needs to be ignited? Or is there some other problem?

No pilot on a heat pump. All you can do is make sure the circuit breaker in the electric panel is turned on. If that is OK call a local HVAC company for repair.

For temporary heat you might set the thermostat to emergency heat if that setting is available or turn the thermostat all the way up kicking in the second stage electric heat.