Transformer and Amplifier: Not same thing!

A step up Transformer basically increases the magnitude of primary applied voltage that is
increases the amplitude of voltage wave form. A voltage amplifier does exactly the same. 

Than a very strange but thinkable question comes what is the difference between the two and can we use a small step up transformer in place of voltage amplifier and vice-versa?

Transformer basically changes the current and voltage keeping the power constant whereas amplifier focus on voltage or current amplification taking Dc as input. 

You buy a transformer, you can't change its gain.  You have to physically modify the transformer by changing the number of coils in order to change its gain.

What matters is power gain, not current or voltage gain independently. A transistor can give power gain whereas transformer can not. 

A transistor can take almost all shapes of input, a transformer can't. For example, transistor works on DC input, transformer don't.

You buy a transistor, though, and you can change its voltage gain by switching resistors, or you can use it as a switch, use it to amplify current instead of voltage, or go unstable and oscillate, or any number of a range of functions.

Salient difference between Transformer and Amplifier

Transformer	Amplifier
Transformers are unable to amplify (step up) an ac input Voltage without reducing (stepping down) it`s current capability.	Amplifier can amplify both current and Voltage at the same time. We can have 1V at 1uA to drive the input but might also get many volts at many Amps at the output.
Transformer`s coil windings never requires a dc Voltage to operate. Sometimes a dc Voltage might be present in a transformer winding for auxiliaries but the dc is not required for the operation of the transformer.	Amplifier almost always requires a dc working supply Voltage to operate. Amplifier is active element
Transformer has more winding added to its secondary winding to obtain Voltage amplification.	An Amplifier actually modulates a fixed dc source Voltage in response to an ac input Voltage to obtain output Voltage amplification.
A transformer`s input current is proportional to its load current.	Amplifier’s input current is normally almost independent of its load current.
A transformer is like a gearbox, whereas an amplifier is like an engine. The gearbox converts energy like a transformer.	Amplifier is like an engine, which consumes fuel to give output. Similarly amplifier consumed DC supply to give output.
A step up transformer can amplify a specified type of input which is the sinusoidal input or time varying input and add to that the range of input the transformer is very flexible in range.	Amplifier can amplify any signal and while the amplifier would have a limited range then in the saturation state.
In an ideal transformer output impedance is equal to the source impedance times the square of the turns ratio.	An amplifier can have output impedance that is independent of the source impedance.