Buffer Amplifier using LM339

I"m having trouble getting my buffer amplifier to work correctly.

I'm using an LM339 op amp with 5 V Vcc.

The buffer amplifier I'm building is the standard voltage buffer amplifier: https://upload.wikimedia.org/wikipedia/commons/thumb/f/f7/Op-Amp_Unity-Gain_Buffer.svg/220px-Op-Amp_Unity-Gain_Buffer.svg.png

However, I am getting 5 V at the input, but the output is giving me about 0.4 V, measuring using a DMM. Shouldn't the buffer work with any op amp?

Any ideas?

The reason it doesn't work is that the LM339 is not an OpAmp. It is a quad comparator with open collector outputs.

Oh ok. Is there another opamp that i can use with a single 5 V Vcc?

What range of input and output voltages do you need? Max bandwidth (Frequency)? ie: What do you intend to use it for?
Look for a rail to rail OpAmp if you want 0-5V inputs and outputs while using a single 5V supply. Example: MCP6001, TLV2474, etc.