def search_entities(raw_text_string, search):
    """Searches for known entities in a string.
    
    Helper function for construct_entity_conet(). Iterates over a list
    of entities and looks to see if they are present in a given text
    string. If they are, then it will append the entity to a list for
    each text. These lists of ents appearing in texts can be used to
    construct a network of entities that co-occurr within texts.
    """
    ents = []
    for entity in search:
        if entity.lower() in raw_text_string.lower():
            ents.append(entity.lower())
    return ents