Like most things, search engines are not going to tell you exactly how this is done, however it is widely accepted that Twitter profiles are scored by search engines to ascertain their authority. The more authoritative a profile, the more likely it is to signal to search engines that what is being tweeted is worthwhile content and should be displayed more predominantly in search results.
So what makes an authoritative Twitter profile? Well again there’s no definitive answer, but there is a general consensus that the following help determine a profile’s authority:
Number of followers
Authority of followers
Regularity of updates on account
Age of profile
Follower to following ratio
Amount of tweets being re-tweeted
Authority of accounts re-tweeting your tweets
So in summary, what this all boils down to is trust. Is your profile trustworthy enough for search engines to take into account what you’re Tweeting about when determining rankings.
Look at addressing the above points by regularly updating your profile and grow your own following by tweeting about unique worthwhile content. Doing so should give your own Twitter profile that much more influence over rankings.
More information on how Twitter can effect rankings: