How do I measure the effectiveness of my social media marketing on Facebook?

I think the two metrics to keep an eye on, on a day-to-day basis are engaged users and virality.
If you are a Facebook page admin, these metrics are easily available to you on Facebook Insights.
These are more important that Likes because they are inclusive of actions including Likes/commenting/sharing.

i trust your audience's engagement is a key metric when measuring the effectiveness of your FB page social media marketing strategy.
Basically, you'd need to ensure: 1) the content you are sharing on daily basis is getting liked, shared, commented on by users within a reasonable timeframe 2) whatever questions you ask are being answered also within a reasonable timeframe.
3) all comments/ feedback you receive are being actioned/ answered (from your end) within a reasonable timeframe.
Facebook insights can be very helpful when you're trying to measure the metrics, but keep it real, transparent and proactive, that does it for you.

I agree with Peggy, I personally think that the interaction of Facebook users to the posts and their engagement towards the page are the most important tools to measure the effectiveness of my Facebook page.
If people are interested in the content I'm offering them on daily basis, they will be interested in coming back and checking the page several time per day.

Engagement, likes, social interaction, conversation flow are all metrics one can use to assess the effectiveness of social media marketing on Facebook.
Social space is very exciting and innovative and could become a myth if we are not clear on the objectives set so we are able to measure the effectiveness of activities.

Relying only on the number of likes to measure your Facebook marketing success is a bit of a misstep. While likes give a hint of your audience size, they’re just the tip of the iceberg. I dig into metrics like engagement rates (likes, comments, shares), reach and impressions to see how widely and effectively your content is spreading. Click-through rates tell me how well your posts drive traffic, and conversion rates show how many people are taking the actions you want. Also, checking the ROI helps me understand if the costs are paying off. To get a true sense of success, mix all these metrics together and align them with your business goals.

1-Shares
2- Comments
3- Feeds Back
4- Ideas Purposed

Number of users/Likes is not basically the matter but the major & the most essential phase where the internet marketing expert has to focus in Social Media Management is that, its not only the matter of branding but to make it the most successful community where the users would love to engage with it frequently.
This will really gauge your true success in Social Media Marketing.
Have a Nice Day.
Syed Waqas Saghir Internet Marketing Expert, SEO Consultant, Social Media Evangelist.
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its determine what percentage of total leads come from facebook, and break this data down for each facebook page. track and compare how many leads you get per follower on your various pages to determine where you're being the most effective.

I personally think that the interaction of Facebook users to the posts and their engagement towards the page are the most important tools to measure the effectiveness of my Facebook page

all comments/ feedback you receive are being actioned/ answered (from your end) within a reasonable timeframe. Facebook insights can be very helpful when you're trying to measure the metrics, but keep it real, transparent and proactive, that does it for you.