Yes. You are always the best advocate for your work, including on social media platforms, whether you are a published author or looking for a publisher. These days, there are many editors on social media who use these platforms for discovery and outreach, so it is always a good idea to build your visibility.
This visibility is also important when your book is published, and you should seize the opportunity to promote your book to your network of friends, families, and peers. All of the things you do on social media—tweeting, updating on Facebook, and posting on Instagram—can add up to make a big difference in the overall attention your book can receive. This does not mean that you have to go it alone; many university presses also have active social media accounts on many platforms. You can often re-post something that the press has posted about your book and vice versa. Always be sure to tag your press when you are doing social media posts, as cross-postings are one of the ways that word can spread. Be sure to check in with your press if you are active on social media, as they are likely happy to know that and will seek to include you in their online promotions.