As Facebook grows, expect to see more ads on Instagram

If you're starting to notice more ads on Instagram, it's all part of Facebook's plan.

Facebook, the world's largest social network, has steadily built its advertising business to become the world's second-largest digital ad platform after Google. Now it's looking at ways to make more money from video ads and from newer services like Instagram, the mobile photo-sharing app that it bought for $1 billion in 2012.

Instagram recently announced it has over 400 million monthly users, surpassing the 300 million who use the rival social networking site Twitter. While Facebook has been introducing Instagram ads slowly — to avoid irritating users by overloading them with...