As well as building links to these profile pages, it's recommended that you participate often and thoughtfully in the networks themselves. This activity will also help lift your profile in the search engines. I know this from personal experience. I've seen my Linkedin and Twitter profiles rise up the rankings for searches for my name after I was active on them for a while.
To this end, commenting on blogs is also worth doing. So many blogs now have boxes to put your Twitter handle in. I assume that the majority of such links are "nofollow". But some would be "dofollow", which would help lift the site being linked to search engine wise. (In any case, some blog readers are bound to click on those links and end up following you. So it's worth doing just for that.)