US iPhone app downloads continued to decline in April 2012, with the cost to acquire loyal users increasing, according to an analysis from Fiksu.

The marketing technology company said that movement in the social networking and games categories in Apple’s App Store “introduced new mobile advertising opportunities and heightened competition,” leading to an increase in mobile marketing costs.

According to Fiksu’s measurement of average daily download volumes for the top 200 free iPhone apps in the US, the number dropped by 4.9 percent to 4.23 million, from 4.45 million in March.

Its cost per loyal user index increased by 12.3 percent to US$1.46 from US$1.30 in March.

Micah Adler, Fiksu’s CEO, said that “April's continued downward trajectory of app downloads was expected, as no major events sparked discovery during the month. Additionally, app marketers continued to scale back their use of robotic install tactics in response to Apple's policy on third-party marketing services."

The company previously noted a slowdown in app downloads, falling to 3.8 million in September 2011, before the numbers saw a boost to an all-time high following the introduction of the iPhone 4S.

Adler continued: “we observed more aggressive advertising spending as marketers moved out of the first quarter lull and began to seek new opportunities to compete for rank especially in the dynamic social networking and games categories, which experienced volatility during the month.”