Try these different strategies to promote your Google+ page and gain followers:
Post updates frequently and keep your profile fresh – People are more likely to engage with a page that contains fresh posts and a complete profile. Learn about sharing updates in Google My Business.
Link your Google+ page and your website – This is a great way to drive traffic to a page and it provides an excellent opportunity to engage with your customers and fans. Learn how to link a page and website.
Add the Google+ badge to your website: Grow a page’s followers directly from your website. The badge helps Google consolidate +1's from your website and a Google+ page.
Publish a page's Custom URL: Use it in emails or other offline marketing to help people remember how to get to a page.
Link your Google+ page with your AdWords campaign - Connecting a page to your campaigns allows your advertising and page to share +1's. Any +1's on your ads will increment the count on a page and vice versa. Learn more about social extensions.
Link your Google+ page with your AdWords Express campaign - You can set your AdWords Express destination page to be a Google+ page. Learn more.