Hi,

Our requirement is to create a word cloud (tag cloud) based on most searched keywords in SharePoint.

Any advice in which direction I should proceed. We are having on-premise SharePoint 2013

You can try using the "Top Queries By Day" or "Top Queries By Month" search usage reports. You can find these in the search service application "Usage Reports". You could create a timer job to generate these reports and then use the data to feed your tag cloud.

https://technet.microsoft.com/en-us/library/jj219611(v=office.15).aspx#Proc4