Online job site Monster.com is creating a co-branded help wanted channel with the Boston Globe’s Boston.com, the first major step since striking an ad alliance with the paper’s parent, the New York Times Company in February. The move also reflects the increased competition for revenue from online classifieds, as typified by the dozen entities involved in the Yahoo Newspaper Consortium, which began as co-branding with Yahoo’s HotJobs, and rival CareerBuilder, owned by Gannett, the Tribune Company, McClatchy and Microsoft, which purchased a minority stake in it earlier this month. The co-branded Monster/BostonWorks site claims it will reach 70 percent of the job-seeking market in that area. According to a spokesman for Monster, a co-branded site with the NYT is scheduled to launch next month. Since February, Monster has helped start co-branded sites with three small newspapers including one in Worcester, MA., and two Florida papers in Lakeland and Sarasota.