American Midstream Partners LP, which owns and operates a diversified portfolio of natural gas midstream assets, filed on Thursday with the SEC to raise up to $75 million in an initial public offering. The Denver, CO-based company, which was founded in 2009 and booked $212 million in sales last year, plans to list on the NASDAQ. Citi and BofA Merrill Lynch are the lead underwriters on the deal. No pricing terms were disclosed.