But how can i search this log in search-string?
It depends on what source and sourcetype you chose when setting up the input. source will likely be tcp:80 so:
Please check your settings.
Splunk > Manager » Data inputs » TCP
You should have set up sourcetype and host if "TCP Data Inputs". Do you use in any applications "local forwarder"?
Do you find from Hosts summary of the search?
Splunk > Search » Summary » Hosts