looking for external speaker to amplify my Macbook pro 13" mid 2012

I'm looking for speakers, but every site I go to only refers to the internal speakers. Are there any speakers that can be attached with a USB?

Yes. Apple hardware and macOS support USB audio out of the box. Plug in amplified or non-amplified devices that fit your room and sound preference and enjoy. USB is digital out so may be better than analog audio out connectors or Bluetooth or AirPlay sounds.

Search for USB Computer Speakers online. If you are totally lost, start with a brand like Logitech and buy from them direct if you’re worried about return policies, counterfeit goods or incompatibility.

• https://www.amazon.com/Logitech-S150-Speakers-Digital-Sound/dp/B000ZH98LU

You can get a USB DAC (Digital to Analog Converter) and connect any speaker or audio device to your Mac. I personally use one to connect my iMac to a Bose Wave Radio and in this answer, the user connects a set of the vintage Apple ball speakers to a newer Mac.