If you really want exposure on Social Media you need to showcase your own work. This should include work on your desk in a filing cabinet or wherever it has ended up.
The work you do for your brand or someone else's in theory is unique to that brand and the odd piece of work could end up being unique on a social network if you are lucky. If this happens, then it will more than likely go viral and you then you have hit the jackpot for that piece of work.
My advice to you is to make sure each piece of work has a unique description on each social network. This means if it is a picture, video or anything else make sure you rewrite the content that goes with it.
It is really easy to lose focus of the main purpose if you decide to promote on every Social network at once. It is better building one up slowly and then moving on to the next one and repeat the process, but also show to be active on the ones you built up sparingly.