heroku drains:add syslog+tls://splunk-server.com:514 -a app_name
And then login into your splunk server and search for any number of logs. I am using Splunk and this is working perfectly fine for me.
Second option - You can purchase add on to your App, like given below: (I haven't used these options, however these are the available ones).
Timber.io
Sumo Logic
LogEnteries
Log DNA
Papertrail
You can also have a look at below options: If you want to have your
logs in JSON format, as it will help if your are pushing your logs to
external system like Splunk/ELK, it would become easy (performance
wise also) to search in JSON.