There are different ways which can help you in tracking ROI from your influencer marketing efforts.
First of all, ROI is money. This means, all the metrics mentioned before are just additional metrics, but they are not equal to the return of investments. All liked, comments and followers don't necessarily bring you money.
So, how to measure influencer marketing ROI?
First, count the income. Use Google Analytics to track the traffic sources, use UTM links to make it even better. Use separate landings and everything you can to separate influencer marketing's traffic from all the other sources. Ideally, you should track every single influencer to understand the ROI of every dollar you pay,