Ongoing social media marketing

I have a website that gives away free stock photos. The site has been around for years and it gets quite a bit of traffic, but we've never done a good job promoting the site via social media and it's time to improve the effort. We need help getting the word out to people who can use our images. We give away tens of thousands of great photos for nearly any use. Our preferred audience is graphic designers, web and social media marketers, web designers, startups, journalists, bloggers, teachers and other image consumers. We have accounts on Facebook, Twitter and Instagram - the goal will be to both increase our following and drive visitors from social media platforms to our main site. We would like this to be an ongoing relationship that continues month after month for the foreseeable future. We give away photos, so we don't have a huge budget, but there is some money to spend on someone who consistently gets good results. We have stock images - you'd be taking stock images from the site and creating content around current events and holidays to promote the site. So in advance of Valentine's day, we should start promoting images on the site related to that holiday. Plus promote stock photography news in general, design tools that would be of interest to our audience, etc. as appropriate on each platform. You get the idea - expand our social media footprint and make it work. If you're interested, message me for the site and ask questions. Let me know what markets you have successfully worked with. Proposals must imply that you have read this. Thanks for your interest.