I am actually looking for the same thing right now and stumbled across your request. I am a self taught full-stack dev but I like to focus mostly on back end development. My biggest weakness is doing front end design and making things look "pretty" so I was thinking of teaming up with a junior front end dev to fill in the gaps.
Right now I am just looking for someone to help develop personal projects and build a portfolio like you mentioned.
What kind of work do you like to do?