Looks like the Twitter API puts hash tags into the following JSON:
"entities":
{ "hashtags":[],
"urls":[],
"user_mentions":[]
}
You could use EvaluteJsonPath to extract the value of the hashtags into FlowFile attributes, and then use RouteOnAttribute to route the ones matching your tag to a PutFile processor.
This blog shows an example of extracting values from the Twitter JSON and making routing decisions:
https://blogs.apache.org/nifi/entry/indexing_tweets_with_nifi_and