Apart from a few single-day dips this month, Mitt Romney leads the Republican presidential primary candidates in new Facebook Likes per day, according to our Inside Facebook Election Tracker.

This week Newt Gingrich had several days of negative fan growth, losing as many as 50 Likes in a day. Although Gingrich has scaled back on his campaign, he tells the press that he will stay in the race until Romney gets the 1,144 convention delegates he needs to win the nomination. Despite winning decisively in Louisiana on March 24, Rick Santorum saw his rate of new fans decline this week. Ron Paul has also lost momentum.

With today’s mandatory conversion to Timeline for pages, we can see new insights about the demographics of each candidate’s fans. Santorum’s most popular city is Pittsburg, Pa. Santorum served as U.S. senator for Pennsylvania from 1995 to 2007. The majority of Santorum’s fans are between 35 and 54 years old. Gingrich’s fans are concentrated in the 45 to 54 age range and his most popular city is Atlanta, Ga. He grew up in Georgia and served in the House of Representatives for the state. Paul’s most popular city is Houston, Texas. He serves in the U.S. House on behalf of Texas’ 14th district. His fans skew younger than others, with most of them in the 25 to 35 range. Romney, as we noted two weeks ago when he switched to Timeline early, has the most fans in Salt Lake City, Utah, between the ages of 45 and 54.