1) twollow processes new keywords on the next update. Premium updates are hourly. Free accounts updates are every 8 hour due to volume.
2) Your keyword may be obscure.
3) If you started your free acct prior to May 1 you may want to "close your acct", re-login (recreates your account), and reinput your keywords.
twollow must limit the number of people you follow on each update to protect your account. Twitter has rules regarding the usage of their services and twollow.com respects those rules.
Choosing to autofollow your keyword will tell twollow to take care of telling twitter to follow people using your keywords. Otherwise, we keep a rolling list of possible followers for you to manually choose to follow (click your keyword to see the list).
Sign in and click on "Last people followed".
Look at this page. Updates are MUCH faster. 5 vs 20 keywords.
Should you have any further questions you may contact us at support@twollow.zendesk.com. Typical hours are 8-5 EST Monday-Friday, but we check in a lot on the weekends.